UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549

                                  SCHEDULE TO

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

                                Amendment No. 1
                                Sema Group PLC

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                      (Name of Subject Company (issuer))

                             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
                               Schubert Limited
                                277 Park Avenue
                         New York, New York 10172-2066
                                (212) 350-9400

                                  COPIES TO:

     Sarah Murphy, Esq.                    J. David Kirkland, Jr., Esq.
Freshfields Bruckhaus Deringer                   Baker Botts L.L.P.
      65 Fleet Street                          3000 One Shell Plaza
     London EC4Y 1HS                                910 Louisana
    +44 (20) 7832-7429                           Houston, Texas 77002
                                                   (713) 229-1101
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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

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          Transaction valuation                    Amount of filing fee
                 N/A (1)                                 $0.00 (1)
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(1)  No filing fee is required pursuant to general instruction D of Schedule TO.

[ ]  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

[X]  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: [  ]


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LEHMAN BROTHERS
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Press Release
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Not for release, publication or distribution in or into Australia, Canada or
Japan

For immediate release                                       13 February 2001

                            Recommended Cash Offer

                                      by

                                Lehman Brothers

                                 on behalf of

                           Schlumberger Investments

                (a wholly owned subsidiary of Schlumberger NV)

                                      for

                                   Sema plc

During a public conference call hosted yesterday by Schlumberger in relation to
the recommended cash offer for Sema, the following information was disclosed.

"The acquisition of Sema, a leading diversified IT and business services
company, will accelerate the implementation of Schlumberger's strategy of
providing end to end information solutions to customers in selected growth
markets. Sema will enhance Schlumberger's capabilities and critical mass in
systems integration and the range of IT skills which Schlumberger requires to
serve its present and future customer base. It should also allow Schlumberger to
realise revenue synergies as a result of cross selling its core competencies in
network development and management, IP-based applications, data management,
smart cards and security application products.

Assuming the transaction closes in April 2001, Schlumberger estimates that the
acquisition will be dilutive to First Call consensus estimates for
Schlumberger's 2001 earnings per share by approximately 8% before acquisition
related costs and approximately 13% after acquisition related costs.

With regard to 2003, the acquisition is expected to be neutral to earnings per
share before acquisition related costs and modestly dilutive after acquisition
related costs.

Schlumberger believes that the causes of the recent profitability issues within
Sema have been identified and that appropriate action is being taken to address
those issues. Further, Schlumberger believes significant revenue synergies can
be realised towards the latter part of the year 2002 in each of its core
business verticals: Oilfield Services, Utilities and Wireless
Telecommunications."


The foregoing statements are not intended to imply that Schlumberger's earnings
per share for any period will necessarily exceed or fall below those of any
previous period.

Enquiries

Schlumberger
Rex Ross                         Tel:     +1 212 350 9432
Jean-Francois Poupeau            Tel:     +33 1 4062 1330

Lehman Brothers (Financial Adviser and Broker to Schlumberger)
John McIntyre                    Tel:     + 44 (0) 207 601 0011
Henry Phillips
Peter Warne

Except where the context requires otherwise, capitalized terms used in this
announcement have the same meanings as in the announcement of the recommended
cash offer for Sema issued earlier today.

The availability of the Offer to Sema Shareholders who are not resident in the
United Kingdom may be affected by the laws of the relevant jurisdictions. Sema
Securityholders who are not resident in the United Kingdom should inform
themselves about and observe any applicable requirements.

The Offer will not be made, directly or indirectly, in or into Australia, Canada
or Japan and it may not be accepted in or from Australia, Canada or Japan.
Accordingly, copies of this announcement 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 or distribute this announcement in or into Australia, Canada or Japan.

Schlumberger will be filing a Tender Offer Statement and other related
documentation and Sema will be filing a Solicitation/Recommendation Statement
with the Securities and Exchange Commission on the date the Offer Document is
mailed to Sema's Shareholders. 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 when they
become available as they will contain important information.

This announcement may contain forward-looking statements as defined in the
Private Litigation Reform Act of 1995. These statements by their nature involve
risks and uncertainties and there are many factors which may cause actual
results to differ materially from these statements. Such factors include
economic, competitive and technological factors affecting Schlumberger's and
Sema's operations, markets, services and prices as well as Schlumberger's
ability to integrate Sema's businesses with Schlumberger's and to realise
synergies from the acquisition and the other factors detailed in Schlumberger's
and Sema's SEC filings.

The contents of this document, which have been prepared by and are the sole
responsibilities of Schlumberger Limited, have been approved by Lehman Brothers
for the purposes of section 57 of the United Kingdom's Financial Services Act
1986. Lehman Brothers, which is regulated in the United Kingdom by The
Securities and Futures Authority, is acting for Schlumberger Limited and
Schlumberger Investments in connection with the Offer and will not be
responsible to anyone other than the same for providing the protections afforded
to customers of Lehman Brothers, nor for providing advice in relation to the
Offer.