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                                                                   EXHIBIT 10.30

                                 THIRD AMENDMENT

                  THIRD AMENDMENT, dated as of May 13, 1997 (this "Third
Amendment"), to the Credit Agreement, dated as of September 30, 1996 (as amended
by the Global Amendment and Assignment and Acceptance, dated as of October 9,
1996, the Second Amendment, dated as of April 23, 1997 and as may be further
amended, supplemented or otherwise modified from time to time, the "Credit
Agreement"), among RIGCO NORTH AMERICA, L.L.C., a Delaware limited liability
company (the "Borrower"), the several banks and other financial institutions
from time to time parties thereto (the "Lenders"), LEHMAN COMMERCIAL PAPER INC.
("LCPI"), as Advisor, Syndication Agent and Arranger, HIBERNIA NATIONAL BANK, as
Collateral and Documentation Agent and BHF-BANK AKTIENGESELLSCHAFT, as
Administrative Agent.


                               W I T N E S S E T H

                  WHEREAS, pursuant to the Credit Agreement, the Lenders have
agreed to make, and have made, certain Loans to the Borrower; and

                  WHEREAS, the Borrower has requested that the Lenders amend,
and the Lenders have agreed to amend, certain of the provisions of the Credit
Agreement, upon the terms and subject to the conditions set forth below;

                  NOW, THEREFORE, the parties hereto hereby agree as follows:

                  1. Defined Terms. As used herein, terms defined in this Third
Amendment or in the Credit Agreement are used herein as so defined.

                  2. Amendment to Subsection 5.13. Subsection 5.13 of the Credit
Agreement is hereby amended by deleting the date "May 15, 1997" in the second
line thereof and substituting in lieu thereof the date "June 15, 1997".

                  3. Effectiveness. The amendments provided for herein shall
become effective on the date (the "Effective Date") of satisfaction of the
following condition precedent:

                  (a) The Administrative Agent shall have received counterparts
      of this Third Amendment, duly executed and delivered by the Borrower and
      each of the other parties hereto.

                  (b) All limited liability company and other proceedings, and
      all documents, instruments and other legal matters in connection with the
      transactions contemplated by this Third Amendment shall be satisfactory in
      form and substance to the Arranger and the Administrative Agent.

                  4. Representations and Warranties. After giving effect to the
amendments contained herein, on the Effective Date, the Borrower hereby
confirms, reaffirms and restates the representations and warranties set forth in
Section 3 of the Credit Agreement; provided that each 

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reference in such Section 3 to "this Agreement" shall be deemed to be a
reference both to this Third Amendment and to the Credit Agreement as amended by
this Third Amendment.

                  5. Continuing Effect; No Other Amendments. Except as expressly
amended or waived hereby, all of the terms and provisions of the Credit
Agreement and the other Loan Documents are and shall remain in full force and
effect. The amendments contained herein shall not constitute an amendment or
waiver of any other provision of the Credit Agreement or the other Loan
Documents or for any purpose except as expressly set forth herein.

                  6. No Default. No Default or Event of Default shall have
occurred and be continuing as of the Effective Date after giving effect to this
Third Amendment.

                  7. Costs and Expenses. The Borrower agrees to pay the
reasonable costs and expenses of the Administrative Agent, the Collateral and
Documentation Agent and the Arranger in connection with this Third Amendment,
including without limitation, legal fees and expenses.

                  8. Counterparts. This Third Amendment may be executed in any
number of counterparts by the parties hereto, each of which counterparts when so
executed shall be an original, but all the counterparts shall together
constitute one and the same instrument.

                  9. GOVERNING LAW. THIS THIRD AMENDMENT SHALL BE GOVERNED BY,
AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW
YORK.

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                  IN WITNESS WHEREOF, the parties have caused this Third
Amendment to be duly executed and delivered by their respective proper and duly
authorized officers as of the day and year first above written.

                                   RIGCO NORTH AMERICA, L.L.C.


                                   By:
                                     Title:


                                   BHF-BANK AKTIENGESELLSCHAFT, as 
                                   Administrative Agent and
                                   as a Lender


                                   By:
                                     Title:



                                   By:
                                     Title:


                                   HIBERNIA NATIONAL BANK, as Collateral and 
                                   Documentation Agent and as a Lender


                                   By:
                                     Title:


                                   LEHMAN COMMERCIAL PAPER INC., as 
                                   Syndication Agent and as a Lender


                                   By:
                                     Title:


                                   VAN KAMPEN AMERICAN CAPITAL PRIME
                                   RATE INCOME TRUST


                                   By:
                                     Title:


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                                   PROTECTIVE LIFE INSURANCE COMPANY


                                   By:
                                     Title:

                                   MERRILL LYNCH PRIME RATE PORTFOLIO

                                   By: MERRILL LYNCH ASSET MANAGEMENT 
                                   L.P., as Investment Adviser


                                   By:
                                     Title:

                                   MERRILL LYNCH SENIOR FLOATING RATE
                                   FUND, INC.


                                   By:
                                     Title:

                                   MERRILL LYNCH DEBT STRATEGIES PORTFOLIO

                                   By: MERRILL LYNCH ASSET MANAGEMENT L.P., as 
                                   Investment Adviser


                                   By:
                                     Title:

                                   ML CBO IV (CAYMAN) LTD.

                                   By: Protective Asset Management, L.L.C.,
                                   as Collateral Manager


                                   By:
                                     Title: