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                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549
                             (Amendment No. 1 to)

                                  SCHEDULE TO

           Tender Offer Statement under Section 14(d)(1) or 13(e)(1)
                    of the Securities Exchange Act of 1934


                                   Sema plc
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                      (Name of Subject Company (issuer))

                   Schlumberger N.V. (Schlumberger Limited)
                                Schlumberger BV
                          Schlumberger Industries SA
                           Schlumberger Investments
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                      (Names of Filing Persons--Offeror)

                        Ordinary Shares Nominal Value of 10 pence Each
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                        (Title of Class of Securities)

                                   81661R100
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                     (CUSIP Number of Class of Securities)

                            James L. Gunderson Esq.
                         General Counsel and Secretary
                               Schlumberger N.V.
                                277 Park Avenue
                         New York, New York 10172-2066
                                (212) 350-9400

                                   COPY TO:

                              Sarah Murphy, Esq.
                        Freshfields Bruckhaus Deringer
                                65 Fleet Street
                                London EC4Y 1HS
                              +44 (20) 7832-7429

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          (Name, address, and telephone numbers of person authorized
      to receive notices and communications on behalf of filing persons)


                           CALCULATION OF FILING FEE

================================================================================

        Transaction valuation                      Amount of filing fee
        $788,047,972.60(1)                         $157,609.59(1)(2)

================================================================================
(1)      For purposes of calculating the filing fee pursuant to Rule 0-11(d),
the transaction value of the Sema Shares (including Sema Shares represented by
Sema ADSs) to be received by the Purchaser, assuming full acceptance of the
Offer by holders in the United States, is calculated as follows: 97,325,439 Sema
Shares (including Sema Shares represented by Sema ADSs) multiplied by 560 pence
per Sema Share, the cash consideration being offered per Sema Share, which
yields (Pounds)545,022,458.4, converted at the exchange rate on February 19,
2001 of (Pounds)1=$1.4459, which yields $788,047,972.60, multiplied by 1/50/th/
of 1%, which yields $157,609.59.

(2)  Sent by wire transfer to the SEC on February 21, 2001.

[_]      Check the box if any part of the fee is offset as provided by Rule 0-11
         (a) (2) and identify the filing with which the offsetting fee was
         previously paid. Identify the previous filing by registration statement
         number, or the Form or Schedule and the date of its filing.

         Amount Previously Paid:       N/A        Filing Party:      N/A

         Form of Registration No:      N/A        Date Filed:        N/A

[_]      Check the box if the filing relates solely to preliminary
         communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the
statement relates:

[X]      third-party tender offer subject to Rule 14d-1.

[_]      issuer tender offer subject to Rule 13e-4.

[_]      going-private transaction subject to Rule 13e-3.

[_]      amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results
of the tender offer: [_]



     Item 1.   Summary Term Sheet

     The information set forth in "Summary Term Sheet" in the Offer Document
     dated February 21, 2001 (the "Offer Document") of Schlumberger Investments,
     a company incorporated in England and Wales (the "Purchaser"), a copy of
     which is attached hereto as Exhibit (a)(1), is incorporated herein by
     reference. The Purchaser is owned, directly and indirectly, 100% by
     Schlumberger N.V., a company incorporated in the Netherlands Antilles
     ("Schlumberger"). Schlumberger holds 40% of its interest in the Purchaser
     directly. The remaining 60% is held directly by Schlumberger Industries
     S.A., a company incorporated in France, which is a wholly owned subsidiary
     of Schlumberger B.V., a company incorporated in the Netherlands, which is a
     wholly owned subsidiary of Schlumberger.

     Item 2.   Subject Company Information

     (a)  The name of the subject company is Sema plc, a company incorporated in
          England and Wales ("Sema"). Sema's principal executive office is
          located at 233 High Holborn, London WC1V 7DJ, England, and its
          telephone number is +44 207 830 4444. The information set forth under
          "Letter of Recommendation from the Chairman of Sema" in the Offer
          Document is incorporated herein by reference.

     (b)  This Tender Offer Statement on Schedule TO relates to Purchaser's
          offer to purchase all of the 648,836,258 issued and to be issued
          Shares and ADSs (each ADS representing 2 shares), par value 10 pence
          per share, of Sema (the "Sema Securities"), for 560 pence per share or
          1,120 pence per ADS, net to seller in cash, less any required
          withholding taxes and without interest, upon the terms and subject to
          the conditions of the Offer Document and the related Letter of
          Transmittal ("Letter of Transmittal"), copies of which are attached
          hereto as Exhibits (a)(1) and (a)(2), respectively.

     (c)  The information set forth in "Summary Term Sheet - How does the Offer
          compare with recent prices of Sema Shares?," "Summary Term Sheet -What
          is the market value of my Sema Securities as of a recent Date?" and
          "Appendix IV - Additional Information" in the Offer Document is
          incorporated herein by reference.

     Item 3.   Identity and background of filing person

     The names of the filing persons are Schlumberger Investments, Schlumberger,
     Schlumberger Industries S.A. and Schlumberger B.V. The information set
     forth regarding the first two companies in "Summary Term Sheet - Who is
     buying my shares?," "Letter from Lehman Brothers - Information on
     Schlumberger," "Letter from Lehman Brothers - Information on Schlumberger
     Investments and Schlumberger Industries S.A.," "Appendix IV - Additional
     Information," "Schedule IVA -Information Concerning the Directors of
     Schlumberger Investments" and "Schedule IVB - Information Concerning the
     Directors and Executive Officers of Schlumberger" in the Offer Document is
     incorporated herein by reference. The

                                                                          Page 3


     information for Schlumberger Industries S.A. and Schlumberger B.V. is set
     out below.

(a)  The principal address of Schlumberger Industries S.A. is 50, Avenue Jean
     Jaures 92129, Montrogue, France, and the telephone number is +33 1 47 46 61
     00. The principal address of Schlumberger B.V. is Parkstraat 83-89, 2514
     JG The Hague, the Netherlands, and the telephone number is + 31 70 310
     5400.

(b)  Schlumberger B.V. is a finance and holding company, with activities of a
     commercial, industrial and financial nature.  Activities of Schlumberger
     Industries S.A. are set out in the "Letter from Lehman Brothers" in the
     Offer Document and is incorporated herein by reference.

(c)  Set forth below is the name, present principal occupation or employment and
     material occupations, positions, offices or employments for the past five
     years of each member of the board of directors and each executive officer
     of Schlumberger Industries S.A.

Name and Position with Present Principal Occupation or Employment and Schlumberger Industries S.A. Material Positions Held During the Past Five Years ---------------------------- -------------------------------------------------- Marcel Tournereau Director Real Estate Atlantic Asia and Director of Social Affairs SSSA, Director and Vice President Paris, January 2000 to present. Vice President & General Manager, RPS, Montrouge, September 1997 to January 2000. Director Real Estate Atlantic Asia, Schlumberger, Paris, VP Division Enertec, Velizy, January 1996 to September 1997. Vice President & General Manager, Europe-Africa Unit, Montrouge, March 1994 to January 1996. Business address: Schlumberger, 50 avenue Jean-Jaures, BP 620-01, 92542 Montrouge Cedex, France. Business tel.: +33 1 4647 6102. Citizenship: France. Date of Birth: October 12, 1947. Philippe Bonnard Vice President, RMS France, November 2000 to present. Director and Vice President Vice President France and Africa Middle East, July 2000 to November 2000. Vice President RMS France, January 1998 to July 2000. General Manager, Water and Heat Metering Europe, November 1993 to January 1998. Business address: Schlumberger RMS, 50 avenue Jean-Jaures, BP 620-03, 92542 Montrouge Cedex, France. Business tel.: + 33 1 47 46 6062. Citizenship: France. Date of Birth: August 25, 1941. Anna Hrayssi Deputy General Counsel - Corporate, 1998 to present. Director and Secretary Legal Department Training Manager, 1997 to 1998. Regional Counsel OFS Europe Africa, 1996 to 1997. General Counsel Dowell Schlumberger, 1995 to 1996. Business address: Schlumberger, 42 rue Saint Dominique, 75007 Paris, France. Business tel.: + 33 1 4062 1251. Citizenship: France. Date of Birth: September 14, 1948.
Page 4 Andre Cornet Retired, July 1, 1994. Director Director of Industrial Affairs (for Schlumberger Industries International) and Chairman of Schlumberger Industries, January 1, 1993 to June 30, 1994. Address: 10, rue Paul Couderc, 9233 Sceaux, France. Tel.: +33 1 4660 6487. Citizenship: France. Date of Birth: January 27, 1934. Joseph Alloul Retired, November 1, 1997. Director Financial Director in charge of the Training & Development for Schlumberger, January 19, 1994 to October 31, 1997. Address: Ile Saint Germain, 7 rue Jean Monet, 92130 Issy-les-Moulineaux, France. Tel.: +33 2 3188 6396. Citizenship: France. Date of Birth: August 13, 1936. Jacques Biscay Retired, April 1, 1996. Director Director of Personnel SL Paris, 1993 to March 31, 1996. Address: 3 rue des Dardanelles, 75017 Paris, France. Tel.: + 33 1 4572 3271. Citizenship: France. Date of Birth: December 5, 1933. Jean-Dominique Percevault Vice President - European Affairs, since May 1994. Director and President President - Geco-Prakla, May 1994 and prior. Address: c/o Schlumberger, 277 Park Avenue, New York, New York 10172-0266, USA. Tel.: + 1 212 350 9400. Citizenship: France. Date of Birth: March 26, 1945.
During the last five years, none of Schlumberger Industries S.A. or, to the best of their knowledge, any of the persons listed above (i) has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or (ii) was a party to any judicial or administrative proceeding (except for matters that were dismissed without sanction or settlement) that resulted in a judgment, decree or final order enjoining future violations of, or prohibiting activities subject to, federal or state securities laws or finding any violation of such laws. Set forth below is the name, present occupation or employment and material occupations, positions, offices or employments for the past five years of the sole managing director of Schlumberger B.V. Page 5
Present Principal Occupation or Employment: Name Material Positions Held During the Past Five Years ---- --------------------------------------------------- Abraham Verburg Controller, Schlumberger B.V., February 1994 to present. Director, Schlumberger B.V., February 1994 to present. Business address: Schlumberger B.V., Parkstraat 83-89, 2514 JG The Hague, the Netherlands. Business telephone: +31 70 310 5400. Citizenship: Netherlands. Date of Birth: October 13, 1951.
During the last five years, none of Schlumberger B.V. or, to the best of his knowledge, the person listed above (i) has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or (ii) was a party to any judicial or administrative proceeding (except for matters that were dismissed without sanction or settlement) that resulted in a judgment, decree or final order enjoining future violations of, or prohibiting activities subject to, federal or state securities laws or finding any violation of such laws. Item 4. Terms of the Transaction The information set forth in "Summary Term Sheet - What are the classes and amounts of Sema Securities sought in the Offer?," "Summary Term Sheet -What would I receive in exchange for my Sema Securities?," "Summary Term Sheet - How long do I have to decide whether to accept the offer?," "Summary Term Sheet - Can the Offer be extended and under what circumstances?," "Summary Term Sheet - What is the difference between the Initial Offer Period and the Subsequent Offer Period? Until what time can I withdraw my acceptance?," "Summary Term Sheet - Can the Offer be extended and under what circumstances?," "Summary Term Sheet - How will I be notified if the Offer is extended?," "Summary Term Sheet - What are the most significant conditions to the Offer?," "Summary Term Sheet - How do I accept the Offer?," "Summary Term Sheet - How do I withdraw my acceptance?," "Summary Term Sheet - Will the Offer be followed by a compulsory acquisition?," "Summary Term Sheet - If I decide not to accept, how will the offer affect my securities?," "Summary Term Sheet - Will I be taxed on the cash?," Letter from Lehman Brothers," "Appendix I - Conditions and Further Terms of the Transaction" and Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Item 5. Past contacts, transactions, negotiations and agreements The information concerning Schlumberger Investments and Schlumberger set forth in "Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Neither Schlumberger Industries S.A. nor Schlumberger B.V., or, to the best of their knowledge, any of the persons listed in Item 3 above, has any contract, arrangement, understanding or relationship with any other person with respect to any securities of Sema, including but not limited to, any contract, arrangement, understanding or Page 6 relationship concerning the transfer or voting of such securities, joint ventures, loan or option arrangements, puts or calls, guarantees of loans, guarantees against loss or the giving or withholding of proxies. Neither Schlumberger Industries S.A. nor Schlumberger B.V. or, to the best of their knowledge, any of the persons listed in Item 3 above, has had any business relationship or transaction with Sema or any of its executive officers, directors or affiliates that is required to be reported under this Schedule TO. There have been no contacts, negotiations, transactions between Schlumberger Industries S.A. or Schlumberger B.V. or any of the persons listed in Item 3 above, on the one hand, and Sema and its affiliates, on the other hand, concerning a merger, consolidation or acquisition of securities, an election of directors or a sale or other transfer of a material amount of assets. Item 6. Purposes of the transaction and plans or proposals The information set forth in "Summary Term Sheet - Why are we making this Offer?," "Summary Term Sheet - If I decide not to accept, how will the offer affect my securities?," "Letter of Recommendation from the Chairman of SEMA," "Letter from Lehman Brothers," "Schlumberger Press Release on the Financial Effect of the Offer" and "Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Item 7. Sources and amount of funds or other consideration The information set forth in "Summary Term Sheet - Do you have the financial resources to make payment?," "Letter of Recommendation from the Chairman of SEMA," "Letter from Lehman Brothers" and "Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Item 8. Interests in securities of the subject company The information regarding Schlumberger Investments and Schlumberger set forth in "Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Neither Schlumberger Industries S.A. nor Schlumberger B.V. or, to the best of their knowledge, any of the persons listed in Item 3 above, or any associate (as such term is defined for the purposes of the Exchange Act) beneficially owns or has any right to acquire, directly or indirectly, any equity securities of Sema, and neither Schlumberger Industries S.A. nor Schlumberger B.V. or, to the best of their knowledge, any of the persons listed in Item 3 above, has effected any transaction in such equity securities during the past sixty days. Item 9. Persons/assets, retained, employed, compensated or used The information set forth in "Letter from Lehman Brothers," "Appendix I - Conditions and Further Terms of Offer" and "Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Page 7 Item 10. Financial statements of certain bidders Financial statements are not deemed material because the consideration consists solely of cash. Item 11. Additional Information The information set forth in "Appendix IV - Additional Information" in the Offer Document is incorporated herein by reference. Item 12. Exhibits (a)(1) Offer Document dated February 21, 2001.** (a)(2) Form of Letter of Transmittal.** (a)(3) Form of Notice of Guaranteed Delivery.** (a)(4) Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.** (a)(5) Form of Acceptance, Authority and Election.** (a)(6) Form of Letter to Clients for use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.** (a)(11) Press Release issued by Schlumberger Investments, dated February 21, 2001.** (a)(12) Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9.** (a)(13) Form of Summary Advertisement in The Wall Street Journal, dated February 21, 2001.** (a)(14) Form of Summary Advertisement in the Financial Times, dated February 22, 2001. (b)(1) Credit Facility, dated February 20, 2001, between (1) Schlumberger; (2) Schlumberger Industries S.A.; (3) Schlumberger PLC; (4) Schlumberger Investments; (5) JP Morgan Plc, BNP Paribas, Salomon Brothers International Limited and Lehman Brothers International (Europe) (each as arrangers), Citibank International Plc as facility agent, and The Chase Manhattan Bank, BNP Paribas Citibank, N.A., and Lehman Commercial Paper Inc.** Page 8 (c) Not applicable. (d)(1) Inducement Fee Letter Agreement, dated February 12, 2001, between Schlumberger Investments and Sema.** (d)(2) Director Undertaking, dated February 11, 2001, from Veronica Oswald to Schlumberger.** (d)(3) Director Undertaking, dated February 11, 2001, from Sir Julian Oswald to Schlumberger.** (d)(4) Director Undertaking, dated February 11, 2001, from Pierre Bonelli to Schlumberger.** (d)(5) Director Undertaking, dated February 11, 2001, from William Bitan to Schlumberger.** (d)(6) Director Undertaking, dated February 11, 2001, from Gilles Cosson to Schlumberger.** (d)(7) Director Undertaking, dated February 11, 2001, from Herve Couffin to Schlumberger.** (d)(8) Director Undertaking, dated February 11, 2001, from Pascal Viginier to Schlumberger.** (d)(9) Director Undertaking, dated February 11, 2001, from Frank Jones to Schlumberger.** (d)(10) Director Undertaking, dated February 11, 2001, from Harry Fryer to Schlumberger.** (d)(11) Director Undertaking, dated February 11, 2001, from Tidu Maini to Schlumberger.** (d)(12) Director Undertaking, dated February 11, 2001, from Didier Pineau- Valencienne to Schlumberger.** (d)(13) Director Undertaking, dated February 11, 2001, from George Schmitt to Schlumberger.** (d)(14) Irrevocable Undertaking, dated February 12, 2001, from Paribas Affaires Industrielles to Schlumberger Investments and Lehman Brothers Europe Limited.** (d)(15) Irrevocable Undertaking, dated February 12, 2001, from France Telecom S.A. to Schlumberger Investments and Lehman Brothers Europe Limited.** (d)(16) Power of Attorney of Schlumberger Investments and Schlumberger.** Page 9 (e) Not applicable. (f) Not applicable. (g) Not applicable. (h) Not applicable. * Previously filed with the Schedule TO filed on February 12, 2001 or with Amendment No. 1 to the Schedule TO filed on February 13, 2001. ** Previously filed with the Schedule TO filed on February 21, 2001. Page 10 Signatures After due inquiry and to the best of our knowledge and belief, the undersigned hereby certify that the information set forth in this amendment to the tender offer statement is true, complete and correct. Dated: February 22, 2001 SCHLUMBERG INVESTMENTS SCHLUMBERGER N.V. By: /s/ ELLEN SUMMER By: /s/ ELLEN SUMMER ---------------- ----------------- Name: Ellen Summer Name: Ellen Summer Title: Authorized Signatory Title: Authorized Signatory Page 11 Signatures After due inquiry and to the best of our knowledge and belief, the undersigned hereby certify that the information set forth in this amendment to the tender offer statement is true, complete and correct. Dated: February 22, 2001 SCHLUMBERGER INDUSTRIES S.A. SCHLUMBERGER B.V. By: /s/ JEAN-DOMINIQUE PERCEVAULT By: /s/ ABRAHAM VERBURG ----------------------------- ------------------- Name: Jean-Dominique Percevault Name: Abraham Verburg Title: President Title: Sole Managing Director Page 12 INDEX TO EXHIBITS Number Exhibit - ------ ------- (a)(1) Offer Document dated February 21, 2000.** (a)(2) Form of Letter of Transmittal.** (a)(3) Form of Notice of Guaranteed Delivery.** (a)(4) Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.** (a)(5) Form of Acceptance, Authority and Election.** (a)(6) Form of Letter to Clients for use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.** (a)(7) Press Release announcing the Recommended Cash Offer by Schlumberger Investments for Sema plc, dated February 12, 2001.* (a)(8) Short Form Press Release announcing Recommended Cash Offer by Schlumberger Investments for Sema plc, dated February 12, 2001.* (a)(9) Additional Offer Update by Schlumberger Investments for Sema plc, dated February 12, 2001.* (a)(10) Press Release issued by Schlumberger Investments, dated February 13, 2001.* (a)(11) Press Release issued by Schlumberger Investments, dated February 21, 2001.** (a)(12) Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9.** (a)(13) Form of Summary Advertisement in The Wall Street Journal, dated February 21, 2001.** (a)(14) Form of Summary Advertisement in the Financial Times, dated February 22, 2001. (b)(1) Credit Facility, dated February 20, 2001, between (1) Schlumberger; (2) Schlumberger Industries S.A.; (3) Schlumberger PLC; (4) Schlumberger Investments; (5) JP Morgan Plc, BNP Paribas, Salomon Brothers International Limited and Lehman Brothers International (Europe) (each as arrangers), Citibank International Plc as facility agent, and The Chase Manhattan Bank, BNP Paribas Citibank, N.A., and Lehman Commercial Paper Inc.** (d)(1) Inducement Fee Letter Agreement, dated Februay 12, 2001, between Schlumberger Investments and Sema.** (d)(2) Director Undertaking, dated February 11, 2001, from Veronica Oswald to Schlumberger.** (d)(3) Director Undertaking, dated February 11, 2001, from Sir Julian Oswald to Schlumberger.** (d)(4) Director Undertaking, dated February 11, 2001, from Pierre Bonelli to Schlumberger.** (d)(5) Director Undertaking, dated February 11, 2001, from William Bitan to Schlumberger.** (d)(6) Director Undertaking, dated February 11, 2001, from Gilles Cosson to Schlumberger.** (d)(7) Director Undertaking, dated February 11, 2001, from Herve Couffin to Schlumberger.** (d)(8) Director Undertaking, dated February 11, 2001, from Pascal Viginier to Schlumberger.** (d)(9) Director Undertaking, dated February 11, 2001, from Frank Jones to Schlumberger.** (d)(10) Director Undertaking, dated February 11, 2001, from Harry Fryer to Schlumberger.** (d)(11) Director Undertaking, dated February 11, 2001, from Tidu Maini to Schlumberger.** (d)(12) Director Undertaking, dated February 11, 2001, from Didier Pineau- Valencienne to Schlumberger.** (d)(13) Director Undertaking, dated February 11, 2001, from George Schmitt to Schlumberger.** (d)(14) Irrevocable Undertaking, dated February 12, 2001, from Paribas Affaires Industrielles to Schlumberger Investments and Lehman Brothers Europe Limited.** (d)(15) Irrevocable Undertaking, dated February 12, 2001, from France Telecom S.A. to Schlumberger Investments and Lehman Brothers Europe Limited.** (d)(16) Power of Attorney of Schlumberger Investments and Schlumberger.** * Previously filed with the Schedule TO filed on February 12, 2001 or with Amendment No. 1 to the Schedule TO filed on February 13, 2001. ** Previously filed with the Schedule TO filed on February 21, 2001.


                                                              Exhibit 99(a) (14)

                            Recommended Cash Offer
                                      by
                               Lehman Brothers
                                 on behalf of
                           Schlumberger Investments
               (a wholly-owned subsidiary of Schlumberger N.V.)
                                     for
                                   Sema plc

Lehman Brothers announces that it is making a recommended cash offer (the
"Offer"), on behalf of Schlumberger Investments, a wholly-owned subsidiary of
Schlumberger N.V. ("Schlumberger"), to acquire the entire issued and to be
issued share capital of Sema plc ("Sema"). The full terms and conditions of the
Offer (including details of how the Offer may be accepted) are set out in the
offer document dated 21 February 2001 (the "Offer Document") and the Acceptance
Forms. Terms defined in the Offer Document have the same meanings in this
advertisement.

A Sema Securityholder who validly accepts the Offer will receive 560 pence in
cash for each Sema Share and 1,120 pence in cash for each Sema ADS (each ADS
representing 2 Sema Shares).

The Offer values the entire issued and to be issued share capital of Sema at
approximately (Pounds)3.6 billion (US$5.3 billion) (fully diluted for the
exercise of all outstanding options under the Sema Share Option Schemes).

Copies of the Offer Document and the Form of Acceptance are available for
collection in the UK from Computershare Services PLC, PO Box 859, The
Pavillions, Bridgewater Road, Bristol BS99 1XZ or Computershare Services PLC,
7th Floor, Jupiter House, Triton Court, 14 Finsbury Square, London EC2A 1BR and
in the US from Computershare Trust Company of New York, Wall Street Plaza, 88
Pine Street, 19th Floor, New York, NY 10005. Copies of the Offer Document and
the Letter of Transmittal are available for collection in the US from D F King &
Co., Inc., 77 Water Street, New York, NY 10005.

The Offer is made to all Sema Shareholders including those to whom the Offer
Document may not be despatched who hold Sema Shares, or who are entitled to have
Sema Shares unconditionally allotted or issued to them. In conjunction with the
offer being made to Sema Shareholders an offer is being made to holders of Sema
ADSs.

The Offer will initially be open for acceptance until 3.00 p.m. (London time),
10.00 a.m. (New York City time), on 21 March 2001. Schlumberger Investments has
reserved the right (but is not obliged, other than as may be required by the
City Code or the Exchange Act) at any time or from time to time to extend the
Offer.

As set out in the Offer Document, the Sema Board, which has been so advised by
Credit Suisse First Boston (Europe) Limited ("Credit Suisse First Boston") and
NM Rothschild & Sons Limited ("Rothschild"), considers the terms of the Offer to
be fair and reasonable. In providing advice to the Sema Board, Credit Suisse
First Boston and Rothschild have taken into account the Sema Board's commercial
assessments. Accordingly, the Sema Directors unanimously recommend Sema
Securityholders to accept the Offer. The Sema Directors have irrevocably
undertaken to accept the Offer in respect of their own beneficial holdings
comprising 497,742 Sema Shares in aggregate, representing approximately 0.1 per
cent. of Sema's existing issued share capital on 16 February 2001. In addition,
France Telecom and Paribas Affaires Industrielles (a division of BNP Paribas)
have undertaken to accept the Offer in respect of their holdings of 103,634,296
and 31,113,792 Sema Shares, respectively, representing approximately 22 per
cent. in aggregate of Sema's existing issued share capital. Subject to the right
for Schlumberger Investments to improve upon the price of any competing offer,
the undertakings from France Telecom and Paribas Affaires Industrielles in
respect of Sema Shares will cease to be binding if a competing offer is made at
a price in excess of 600 pence per Sema Share, before the end of the day falling
17 days after the Offer Document is posted.

The Offer is not being made, directly or indirectly, in or into Australia,
Canada or Japan and may not be accepted in or from Australia, Canada or Japan.
Accordingly, this advertisement and copies of the Offer Document, the Acceptance
Forms and related documents are not being, and must not be, mailed or otherwise
distributed or sent in or into Australia, Canada or Japan. Custodians, nominees
and trustees should observe these restrictions and should not send this
advertisement, the Offer Document, the Acceptance Forms or any related documents
in or into Australia, Canada or Japan.

Lehman Brothers, Morgan Stanley Dean Witter and Schroder Salomon Smith Barney,
each of which is regulated in the UK by The Securities and Futures Authority
Limited, are acting for Schlumberger, Schlumberger Industries S.A. and
Schlumberger Investments and no one else in connection with the Offer and will
not be responsible to anyone other than Schlumberger, Schlumberger Industries
S.A. and Schlumberger Investments for providing the protections afforded to
customers of Lehman Brothers, Morgan Stanley Dean Witter and Schroder Salomon
Smith Barney, respectively, nor for giving advice in relation to the Offer.
Lehman Brothers, as dealer manager for the Offer, is making the Offer in the
United States on behalf of Schlumberger Investments.

Credit Suisse First Boston and Rothschild, each of which is regulated in the UK
by The Securities and Futures Authority Limited, are acting for Sema and no one
else in connection with the Offer and will not be responsible to anyone other
than Sema

                                    Page 1


for providing the protections afforded to customers of Credit Suisse First
Boston and Rothschild, respectively, nor for giving advice in relation to the
Offer.

The directors of Schlumberger Investments listed in Schedule IVA of the Offer
Document accept responsibility for the information contained in this
advertisement and, to the best of their knowledge and belief (having taken all
reasonable care to ensure that such is the case), the information contained in
this advertisement is in accordance with the facts and does not omit anything
likely to affect the import of such information. This statement is included
solely to comply with Rule 19.2 of the City Code and shall not be deemed to
establish or expand liability under law, including under US federal securities
laws or under the laws of any state of the US.

It should be noted that by virtue of the conflicting provisions of the City Code
and the US securities laws, the Panel has agreed that the Acceptance Condition
can be structured so that the Offer cannot become or be declared unconditional
as to acceptances until such time as all other Conditions to the Offer have been
satisfied, fulfilled or, to the extent permitted, waived. The Acceptance
Condition in paragraph (a) of Appendix I of the Offer Document reflects this.

Schlumberger has also filed a Tender Offer Statement and other related
documentation and Sema has filed a Solicitation/Recommendation Statement with
the Securities and Exchange Commission on 21 February 2001. Free copies of these
documents will be available on the SEC's web site at www.sec.gov. The Tender
Offer Statement may also be obtained at no charge from Schlumberger at 277 Park
Avenue, New York, NY 10172-0266 and the Solicitation/Recommendation Statement
may be obtained at no charge from Sema at Six Concourse Parkway, Suite 2700,
Atlanta, Georgia 30328. Shareholders are urged to read the Tender Offer
Statement, the Solicitation/Recommendation Statement and the related
documentation as they will contain important information.

This announcement is neither an offer to purchase nor a solicitation of an offer
to sell Sema Securities. The Offer is being made solely by the Offer Document
dated 21 February 2001, and the related Acceptance Forms.

22 February 2001

                                    Page 2