EXHIBIT 3.8
 
                                    BYLAWS
                                      OF
                              BMT OF OKLAHOMA, INC.


                                   ARTICLE I
                                   ---------

                                    OFFICES

     Section 1. The registered office shall be in the City of Tulsa, County of 
Tulsa, State of Oklahoma.

     Section 2. The corporation may also have offices at such other places both 
within and without the State of Oklahoma as the Board of Directors may from time
to time determine or the business of the corporation may require.

                                   ARTICLE II
                                   ----------

                           MEETINGS OF SHAREHOLDERS

     Section 1. Meetings of shareholders for any purpose may be held at such
time and place, within or without the State of Oklahoma, as shall be stated in
the notice of the meeting or in a duly executed waiver of notice thereof.

     Section 2. Annual meetings of shareholders, commencing with the year 1987,
shall be held each year at a time and place to be determined by the Board of
Directors, at which meeting they shall elect by a plurality vote by written
ballot a board of directors, and transact such other business as may be properly
brought before the meeting.

     Section 3. Written notice of the annual meeting, stating the place, date
and hour of such meeting, shall be given to each shareholder entitled to vote
thereat not less than ten (10) days nor more than sixty (60) days before the
date of the meeting unless otherwise required by law.

     Section 4. The officer who has charge of the stock ledger of the
corporation shall prepare and make, at least ten (10) days before every meeting
of shareholders, a complete list of the shareholders entitled to vote at the
meeting, arranged in alphabetical order, showing the address of and the number
of shares registered in the name of each shareholder. Such list shall be open to
the examination of any shareholder, for any purpose germane to the meeting,
during ordinary business hours, for a period of at least ten (10) days prior to
the election, either at a place within the city where the meeting is to be held
and which place shall be specified in the notice of the meeting, or, if not
specified, at the place where the meeting is to be held, and the list shall be
produced and kept at the

 
time and place of the meeting during the whole time thereof, and subject to the
inspection of any shareholder who may be present.

     Section 5. Special meetings of the shareholders, for any purpose or
purposes, unless otherwise prescribed by law or by the Articles of
Incorporation, may be called by the Chairman, Vice Chairman or the President and
shall be called by the Chairman, Vice Chairman, President or Secretary at the
request in writing of a majority of the Board of Directors, or at the request in
writing of shareholders owning a majority in amount of the entire capital stock
of the corporation issued and outstanding and entitled to vote. Such request
shall state the purpose or purposes of the proposed meeting.

     Section 6. Written notice of a special meeting of shareholders, stating the
place, date, hour and the purpose or purposes thereof,
shall be given to each shareholder entitled to vote thereat, not less 
than ten (10) days before the date fixed for the meeting unless otherwise
required by law.

     Section 7. Business transacted at any special meeting of the shareholders
shall be limited to the purposes stated in the notice.

     Section 8. The holders of a majority of the shares of stock issued and
outstanding and entitled to vote thereat, present in person or represented by
proxy, shall constitute a quorum at all meetings of the shareholders for the
transaction of business except as otherwise provided by law or by the Articles
of Incorporation. If, however, such quorum shall not be present or represented
at any meeting of the shareholders, the shareholders entitled to vote thereat,
present in person or represented by proxy, shall have power to adjourn the
meeting from time to time, without notice other than announcement at the
meeting, until a quorum shall be present or represented; provided, however, that
if the date of any adjourned meeting is more than thirty (30) days after the
date for which the meeting was originally noticed, or if a new record date is
fixed for the adjourned meeting, written notice of the place, date and hour of
the adjourned meeting shall be given in conformity herewith. At such adjourned
meeting at which a quorum shall be present or represented, any business may be
transacted at the meeting as originally notified.

     Section 9. When a quorum is present at any meeting, the affirmative vote of
the holders of a majority of the shares of stock having voting power present in
person or represented by proxy shall decide any question brought before such
meeting, unless the question is one upon which, by express provision of law or
of the Articles of Incorporation, a different vote is required, in which case
such express provision shall govern and control the decision of such question.

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     Section 10. Each shareholder shall at every meeting of the shareholders be
entitled to one vote in person or by proxy for each share of the capital stock
having voting power held by such shareholder, but no proxy shall be voted or
acted upon after three (3) years from its date unless the proxy provides for a
longer period, and, except where the transfer books of the corporation have been
closed or a date has been fixed as a record date for the determination of its
shareholders entitled to vote, no share of stock shall be voted on at any
election for directors which has been transferred on the books of the
corporation within twenty (20) days preceding such election of directors.

     Section 11. Any action required to or which may be taken at any annual or
special meeting of the shareholders, may be taken without a meeting, without
prior notice and without a vote, if a consent in writing, setting forth the
action so taken, shall be signed by the holders of outstanding stock having not
less than the minimum number of votes that would be necessary to authorize or
take such action at a meeting at which all shares entitled to vote thereon were
present and voted. Prompt notice of the taking of the corporate action by the
shareholders without a meeting by less than unanimous written consent shall be
given to those shareholders who have not consented in writing.

 
                                  ARTICLE III
                                  -----------

                                   DIRECTORS

       Section 1. The number of directors which shall constitute the whole Board
shall be not less than one (1) nor more than seven (7). As of November 7, 1986,
the Board shall consist of 3 directors. Thereafter, within the limits above
specified, the number of directors shall be determined by resolution of the
Board of Directors or by the shareholders at the annual or a special meeting of
the shareholders. Except for the election held by the incorporator(s) and except
as provided in Section 2 and in Section 14 of this Article II, the directors
shall be elected at the annual meeting of shareholders. Each director elected
shall hold office until such director's successor is elected and qualified, or
until such director's earlier resignation or removal. Directors need not be
shareholders.

       Section 2. Except as provided in Section 14 of this Article II, vacancies
and newly created directorships resulting from any increase in the authorized
numbers of directors by the directors may be filled by a majority vote of the
directors then in office, though less than a quorum, and any director so chosen
shall hold office until the next annual election and until such director's
successor is duly elected and qualified, unless such director resigns or is
removed.

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       Section 3. The business of the corporation shall be managed by its Board
of Directors which may exercise all such powers of the corporation and do all
such lawful acts and things as are not by law or by the Articles of
Incorporation or by these Bylaws directed or required to be exercised or done
by the shareholders.

       Section 4. The Board of Directors of the corporation may hold meetings,
both regular and special, either within or without the State of Oklahoma.

       Section 5. Regular meetings of the Board of Directors may be held at such
time and at such place as shall from time to time be determined by the Board.
Five (5) days' notice of all regular meetings shall be given, and such notice
shall state the place, date, hour and the business to be transacted at and
purpose of such meeting.

       Section 6. Special meetings of the Board may be called by the 
President on three (3) days' notice to each director either personally or by
mail or by telegram. Special meetings shall be called by the President or
Secretary in like manner and on like notice on the written request of two (2)
directors unless the corporation has at that time less than three (3) directors,
in which latter event the request of only one (1) director shall be required.
Notice of any special meeting shall state the place, date, hour and the business
to be transacted at and the purpose of such meeting.

       Section 7. At all meetings of the Board, a majority of the directors
shall constitute a quorum for the transaction of business, and the act of a
majority of the directors present at any meeting at which there is a quorum
shall be the act of the Board of Directors, except as may be otherwise
specifically provided by law or by the Articles of Incorporation. If a quorum
shall not be present at any meeting of the Board of Directors, the directors
present thereat may adjourn the meeting from time to time, without notice other
than announcement at the meeting, until a quorum shall be present.
        
     Section 8. The Board of Directors may, by resolution, passed by a majority
of the whole Board, designate one or more committees, each committee to consist
of one (1) or more of the directors of the corporation, which, to the extent
provided in the resolution, shall have and may exercise the powers of the Board
of Directors in the management of the business and affairs of the corporation
and may authorize the seal of the corporation to be affixed to all papers which
may require it. Such committee or committees shall have such name or names as
may be determined from time to time by resolution adopted by the Board of
Directors.

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     Section 9. Each committee shall keep regular minutes of its meetings and
report the same to the Board of Directors when required.
                
     Section 10. Members of the Board of Directors, or of any committee thereof,
may participate in a meeting of such Board or committee by means of conference
telephone or similar communications equipment that enables all persons
participating in the meeting to hear each other. Such participation shall
constitute presence in person at such meeting.

     Section 11. Unless otherwise restricted by the Articles of Incorporation or
these Bylaws, any action required or permitted to be taken at any meeting of the
Board of Directors or any committee thereof may be taken without a meeting, if a
written consent to such action is signed by all members of the Board or of such
committee as the case may be, and such written consent is filed with the minutes
of proceedings of the Board or committee.

     Section 12. The directors may be paid their expenses, if any, of attendance
at such meeting of the Board of Directors and may be paid a fixed sum for
attendance at such meeting of the Board of Directors and/or a stated salary as
director. No such payment shall preclude any director from serving the
corporation in any other capacity and receiving compensation therefor. Members
of special or standing committees may be allowed like compensation for attending
committee meetings.

     Section 13. The Board of Directors at any time may, by affirmative vote of 
a majority of the members of the Board then in office, remove any officer 
elected or appointed by the Board of Directors for cause or without cause.

     Section 14. Any director may be removed, for cause or without cause, by a
majority vote of the shareholders entitled to vote for the election of such
director at any annual or special meeting of the shareholders. Upon such removal
of a director, the shareholders (and not the remaining directors) shall elect a
director to replace such removed director at the same shareholders' meeting at
which such removal took place or at a subsequent shareholders' meeting.

                                  ARTICLE IV
                                  ----------

                                    NOTICES

      Section 1. Notices to directors and shareholders shall be in writing and
delivered personally or mailed to the directors or shareholders at their
addresses appearing on the books of the corporation. Notice by mail shall be
deemed to be given at the time when the same shall be deposited in the United
States 

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mail, postage prepaid. Notice to directors may also be given by telegram. Notice
by telegram shall be deemed to be given when delivered to the sending telegraph
office.

     Section 2. Whenever any notice is required to be given under the provisions
of law or of the Articles of Incorporation or of these Bylaws, a waiver thereof
in writing, signed by the person or persons entitled to such notice, whether
before or after the time stated therein, shall be deemed equivalent to notice.


                                   ARTICLE V
                                   ---------

                                   OFFICERS

     Section 1. The officers of the corporation shall be chosen by the Board of
Directors and shall at a minimum, consist of a President and a Secretary. The
Board of Directors may also choose additional officers, including a Chairman or
Vice Chairman of the Board of Directors, one or more Vice-Presidents who may be
classified by their specific function, a Secretary, a Treasurer and one or more
Assistant Secretaries and Assistant Treasurers. Two or more offices may be held
by the same person, except the offices of President and Secretary.

     Section 2. The Board of Directors at its first meeting and after each
annual meeting of shareholders shall choose a President and a Secretary, and may
choose such other officers and agents as it shall deem necessary.

     Section 3. The salaries of all officers and agents of the corporation shall
be fixed by the Board of Directors.

     Section 4. The officers of the corporation shall hold office until their
successors are chosen and qualify, or until their earlier resignation or
removal. Any vacancy occurring in any office of the corporation shall be filled
by the Board of Directors.
 
     Section 5. The Chairman, or, in the absence of the Chairman, a Vice
 Chairman of the Board, if chosen, shall preside at all meetings of the Board of
 Directors of the corporation and may preside at meetings of the shareholders,
 and shall perform such other duties and have such other powers as the Board of 
 Directors may from time to time prescribe.

     Section 6. Unless the Chairman or Vice Chairman has been so designated 
by the Board of Directors, the President shall be the Chief Executive Officer 
of the Corporation, shall preside at all meetings of the shareholders
and, unless a Chairman or Vice Chairman of the Board has been chosen, at all 
meetings of the Board of Directors, and shall have general and active management
of the business of the corporation and shall see that

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all orders and resolutions of the Board of Directors, are carried into effect. 
The Board of Directors may allocate the duties of President among the Chairman, 
Vice Chairman and the President, to the extent any such other officers are 
elected.

     Section 7. The President (and the Chairman or Vice Chairman, if elected)
shall be empowered to execute bonds, mortgages and other contracts requiring a 
seal, under the seal of the corporation, except where required or permitted by 
law to be otherwise signed and executed and except where the signing and 
execution thereof shall be expressly delegated by the Board of Directors to some
other officer or agent of the corporation. 

     Section 8. The Vice President, or if there shall be more than one, the Vice
Presidents in the order determined by the Board of Directors, shall, in the 
absence of disability of the President, perform the duties and exercise the 
powers of the President and shall perform such other duties and have such other 
powers as the Board of Directors may from time to time prescribe.

     Section 9. The Secretary shall attend all meetings of the Board of
Directors and all meetings of the shareholders and record all the proceedings of
the meetings of the corporation and the Board of Directors in a book to be kept
for that purpose and shall perform like duties for the standing committees when
required. The Secretary shall give, or cause to be given, notice of all meetings
of the shareholders and regular and special meetings of the Board of Directors,
and shall perform such other duties as may be prescribed by the Board of
Directors or President, under whose supervision the Secretary shall be.
Additionally, the Secretary shall have custody of the corporate seal of the
corporation, and the Secretary or an Assistant Secretary, shall have authority
to affix the same to any instrument requiring it, and when so affixed, it may be
attested by the Secretary's signature or by the signature of such Assistant
Secretary. The Board of Directors may give general authority to any other
officer to affix the seal of the corporation and to attest the affixing by
signature.

     Section 10. The Assistant Secretary, or if there be more than one, the
Assistant Secretaries in the order determined by the Board of Directors, shall,
in the absence or disability of the Secretary, perform the duties and exercise
the powers of the Secretary and shall perform such other duties and have such
other powers as the Board of Directors from time to time prescribe.

     Section 11. The Treasurer, if one is chosen or, if not, the Secretary,
shall have the custody of the corporate funds and securities and shall keep full
and accurate accounts of receipts and disbursements in books belonging to the
corporation and shall deposit all moneys and other valuable effects in

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 the name and to the credit of the corporation in such depositories as may be
 designated by the Board of Directors.

     Section 12. The Treasurer, if one is chosen or, if not, the Secretary,
 shall disburse the funds of the corporation as may be ordered by the Board of
 Directors' taking proper vouchers for such disbursements, and shall render to
 the President and the Board of Directors, at its regular meetings, or when the
 Board of Directors so requires, an account of all transactions performed by the
 Treasurer (or Secretary, as the case may be) and of the financial condition of
 the corporation.

     Section 13. The Assistant Treasurer, or if there shall be more than one,
 the Assistant Treasurers in the order determined by the Board of Directors,
 shall, in the absence or disability of the Treasurer, perform the duties and
 exercise the powers of the Treasurer and shall perform such other duties and
 have such other powers as the Board of Directors may from time to time
 prescribe.


                                  ARTICLE VI
                                  ----------

                   CERTIFICATES OF STOCK, TRANSFERS OF STOCK
                         CLOSING OF TRANSFER BOOKS AND
                            REGISTERED SHAREHOLDERS

      Section 1. Every holder of stock in the corporation shall be entitled to
have a certificate, signed by, or in the name of, the corporation by the
Chairman or Vice-Chairman of the Board of Directors, or the President or a Vice-
President, and by the Treasurer or an Assistant Treasurer, or the Secretary or
an Assistant Secretary of the corporation, certifying the number of shares owned
by the shareholder in the corporation.

      Section 2. Any or all the signatures on the certificate may be by
facsimile. In case any officer, transfer agent or registrar who has signed or
whose facsimile signature has been placed upon a certificate shall have ceased
to be such officer, transfer agent or registrar before such certificate is
issued, it may be issued by the corporation with the same effect as if the
person who signed the certificate was such officer, transfer agent or registrar
at the date of issue.

      Section 3. The Board of Directors may direct a new certificate or
certificates to be issued in place of any certificate or certificates
theretofore issued by the corporation alleged to have been lost or stolen or
destroyed, upon the making of an affidavit of that fact by the person claiming
the certificate of stock to be lost, stolen or destroyed. When authorizing such
issue of a new certificate or certificates, the Board of Directors may, in its
discretion and as a condition precedent to the issuance thereof, require the
owner of such lost, stolen or destroyed certificate or certificates, or such
owner's legal 

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representative, to advertise the same in such manner as the
corporation shall require and/or to give the corporation a bond in such sum as
the corporation may direct as indemnity against any claim that may be made
against the corporation with respect to the certificate alleged to have been
lost, stolen or destroyed.

      Section 4. Subject to transfer restrictions permitted by law and to stop
transfer orders directed in good faith by the corporation to any transfer agent
to prevent possible violations of federal or state securities laws, rules or
regulations, upon surrender to the corporation or the transfer agent of the
corporation of a certificate for shares duly endorsed or accompanied by proper
evidence of succession, assignment or authority to transfer, it shall be the
duty of the corporation to issue a new certificate to the person entitled
thereto, cancel the old certificate and record the transaction upon its books.

     Section 5. The Board of Directors may fix a record date, which shall not be
more than sixty (60) nor less than ten (10) days before the date of any meeting
of shareholders, nor more than sixty (60) days prior to the time for the other
action hereinafter described, as of which there shall be determined the
shareholders who are entitled: to notice of or to vote at any meeting of
shareholders or any adjournment thereof; to express consent to corporate action
in writing without a meeting; to receive payment of any dividend or other
distribution or allotment of any rights; or to exercise any rights with respect
to any change, conversion or exchange of stock or with respect to any other
lawful action.

     Section 6. The corporation shall be entitled to treat the person in whose
name any share of stock is registered on the books of the corporation as the
owner thereof for all purposes and shall not be bound to recognize any equitable
or other claim or other interest in such shares in the part of any other person,
whether or not the corporation shall have express or other notice thereof.

                              ARTICLE VII
                              -----------

                           GENERAL PROVISIONS

     Section 1. Dividends upon the capital stock of the corporation, subject to
the provisions of the Articles of Incorporation, if any, may be declared by the
Board of Directors at any regular or special meeting, pursuant to law. Dividends
may be paid in cash, in property or in shares of the corporation's capital
stock.

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     Section 2. There may be set apart out of any of the funds of the
corporation available for dividends such amounts as the Board of Directors deems
proper as a reserve or reserves for working capital, depreciation, losses in
value, or for any other proper corporate purpose, and the Board of Directors may
increase, decrease or abolish any such reserve in the manner in which it was
created.

     Section 3. The Board of Directors shall present at each annual meeting and
at any special meeting of the shareholders when called for by vote of the
shareholders, a full and clear statement of the business and condition of the
corporation.

     Section 4. All checks or demands for money and notes of the corporation
shall be signed by such officer or officers or such other person or persons as
the Board of Directors may from time to time designate.

     Section 5. The fiscal year of the corporation shall be as fixed by the
Board of Directors.

     Section 6. The Board of Directors may provide a suitable seal, containing
the name of the corporation, which seal shall be in charge of the Secretary. If
and when so directed by the Board of Directors or a committee thereof,
duplicates of the seal may be kept and used by the Treasurer or by the Assistant
Secretary or Assistant Treasurer. The seal may be used by causing it, or a
facsimile thereof, to be impressed or affixed or in any other manner reproduced.

     Section 7. The books of account and other records of the corporation may be
kept (subject to any provisions of Oklahoma law) at the principal place of
business or executive offices of the corporation.

                                 ARTICLE VIII
                                 ------------

                    INDEMNIFICATION OF OFFICERS, DIRECTORS,
                             EMPLOYEES AND AGENTS

     To the extent and in the manner permitted by the laws of the State of
Oklahoma, the corporation shall indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit or proceeding, whether civil, criminal, administrative or investigative,
other than an action by or in the right of the corporation, by reason of the
fact that such person is or was a director, officer, employee or agent of the

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corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise against expenses, including attorneys' fees,
judgments, fines and amounts paid in settlement.

                              ARTICLE IX
                              ----------

                              AMENDMENTS

     The Bylaws may be amended or repealed, or new bylaws may be adopted, by the
shareholders or by the Board of Directors at any regular meeting of the
shareholders or of the Board of Directors, or at any special meeting of the
shareholders or of the Board of Directors if notice of such amendment, repeal,
or adoption of new bylaws be contained in the notice of such special meeting.

     APPROVED AND RATIFIED as of this 8th day of November, 1986 by the
undersigned, constituting all of the directors (whether one or more) of the
corporation.


                                      /s/ G. Douglas Fox
                                      ----------------------------
                                      G. Douglas Fox

                                      /s/ Howard G. Barnett, Jr.
                                      ----------------------------
                                      Howard G. Barnett, Jr.

                                      /s/ J. Gary Mourton
                                      ----------------------------
                                      J. Gary Mourton

                                              DIRECTORS


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