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                                                                    EXHIBIT 2.2
 
                                  AMENDMENT TO
                          AGREEMENT AND PLAN OF MERGER
 
     THIS AMENDMENT (the "Amendment") dated as of July 22, 1998 is among Baker
Hughes Incorporated, a Delaware corporation ("Parent"), Baker Hughes Delaware I,
Inc., a Delaware corporation and a direct, wholly owned subsidiary of Parent
("Merger Sub"), and Western Atlas Inc., a Delaware corporation (the "Company").
 
                                    RECITALS
 
     WHEREAS, Parent, Merger Sub and the Company are parties to an Agreement and
Plan of Merger dated as of May 10, 1998 (the "Merger Agreement"); and
 
     WHEREAS, Parent, Merger Sub and the Company wish to amend the Merger
Agreement pursuant to Section 10.5 thereto, and the respective Boards of
Directors of Parent, Merger Sub and the Company have approved and adopted this
Amendment;
 
     NOW, THEREFORE, the parties agree to amend the Merger Agreement as follows:
 
     Section 1. Amendment of the Merger Agreement.
 
     (a) The proviso at the end of Section 4.1(c) of the Merger Agreement is
amended and restated in its entirety to read as follows:
 
     (iv) if the Parent Share Price is greater than or equal to $34.00 but less
     than $38.25, that fraction, rounded to the nearest thousandth, or if there
     shall not be a nearest thousandth, to the next higher thousandth, equal to
     the quotient obtained by dividing $91.80 by the Parent Share Price; and (v)
     if the Parent Share Price is less than $34.00, 2.7.
 
     (b) Section 9.3(d) of the Merger Agreement is deleted.
 
     Section 2. Miscellaneous.
 
     (a) Except as expressly set forth herein, all the provisions of the Merger
Agreement are hereby ratified and confirmed by the parties and shall remain in
full force and effect. All references in the Merger Agreement to "this
Agreement" shall be read as references to the Merger Agreement, as amended by
this Amendment, but references to the date of the Agreement shall remain
references to May 10, 1998.
 
     (b) This Amendment shall be governed by and construed in accordance with
the laws of the State of Delaware, without regarding to its rules of conflict of
laws.
 
     (c) This Amendment may be executed by the parties hereto in separate
counterparts, each of which when so executed and delivered shall be an original,
but all such counterparts shall together constitute one and the same instrument.
Each counterpart may consist of a number of copies hereof each signed by less
than all, but together signed by all of the parties hereto.
 
     (d) Headings of the Sections of this Amendment are for the convenience of
the parties only, and shall be given no substantive or interpretative effect
whatsoever.
 
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     IN WITNESS WHEREOF, the parties have executed this Amendment and caused the
same to be duly delivered on their behalf on the day and year first written
above.
 
                                            BAKER HUGHES INCORPORATED
 
                                            By:      /s/ MAX L. LUKENS
 
                                              ----------------------------------
                                                Name: Max L. Lukens
                                                Title:  Chairman of the Board,
                                                  President and CEO
 
                                            BAKER HUGHES DELAWARE I, INC.
 
                                            By: /s/ LAWRENCE O'DONNELL, III
 
                                              ----------------------------------
                                                Name: Lawrence O'Donnell, III
                                                Title:  Vice President
 
                                            WESTERN ATLAS INC.
 
                                            By:    /s/ WILLIAM H. FLORES
                                              ----------------------------------
                                                Name: William H. Flores
                                                Title:  Senior Vice President
 
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