8-A12B

   1

                                                             Commission File No.



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



                                    FORM 8-A

               FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                    PURSUANT TO SECTION 12(b) OR (g) OF THE
                        SECURITIES EXCHANGE ACT OF 1934


                        MARINE DRILLING COMPANIES, INC.
         (Exact name of registrant as specified in its charter)

                                                        
                          TEXAS                                         74-2558926
         (State of incorporation or organization)                    (I.R.S. Employer
                                                                    Identification No.)

          ONE SUGAR CREEK CENTER BLVD., SUITE 600
                  SUGAR LAND, TEXAS                                     77478-3556
         (Address of principal executive offices)                        (Zip Code)

         


                          Securities to be registered
                     pursuant to Section 12(b) of the Act:

                                                          
                 Title of each class                                     Name of each exchange on
                 to be so registered                                which each class is to be registered
                 -------------------                                ------------------------------------

       Common stock, par value $.01 per share                       New York Stock Exchange
       Preferred share purchase rights                              New York Stock Exchange

       


If this Form relates to the registration of a class of securities pursuant to
Section 12(b) of the Exchange Act and is effective pursuant to General
Instructions A.(c), check the following box.  [X]

If this Form relates to the registration of a class of securities pursuant to
Section 12(g) of the Exchange Act and is effective pursuant to General
Instruction A.(d), check the following box.  [ ]

                          Securities to be registered
                     pursuant to Section 12(g) of the Act:

                                      None
   2


                 INFORMATION REQUIRED IN REGISTRATION STATEMENT

ITEM 1.   DESCRIPTION OF REGISTRANT'S SECURITIES TO BE REGISTERED.

         The class of securities to be registered hereby is the Common stock,
par value $.01 per share (the "Common Stock"), of Marine Drilling Companies,
Inc., a Texas corporation (the "Company") and the associated preferred share
purchase rights (the "Purchase Rights").

         For a description of the Common Stock and the Purchase Rights, see the
information set forth under the caption "Description of Common Stock and
Preferred Stock" in the Prospectus contained in the Registration Statement on
Form S-3 (Registration No. 333-56379), filed by the Company on June 9, 1998,
which is incorporated herein by reference.  Such description is set forth in
Exhibit 1 to this Registration Statement.

ITEM 2.   EXHIBITS.

          1.     Copy of the information set forth under the caption      
                 "Description of Common Stock and Preferred Stock" in the 
                 Prospectus that is included in the Company's Registration
                 Statement on Form S-3, (Registration No. 333-56379).     



                                      2
   3
                                   SIGNATURE

         Pursuant to the requirements of Section 12 of the Securities and
Exchange Act of 1934, the registrant has duly caused this registration
statement to be signed on its behalf by the undersigned, thereto duly
authorized.

                                        MARINE DRILLING COMPANIES, INC.



                                        By   /s/ T. SCOTT O'KEEFE
                                           -----------------------------------
                                        Name:  T. Scott O'Keefe
                                        Title: Senior Vice President
                                               and Chief Financial Officer

Date:  August 7, 1998




                                      3
   4
                              INDEX TO EXHIBITS


EXHIBIT
NUMBER                     DESCRIPTION
- ------                     -----------

  1.      Copy of the information set forth under the caption      
          "Description of Common Stock and Preferred Stock" in the 
          Prospectus that is included in the Company's Registration
          Statement on Form S-3, (Registration No. 333-56379). 
                                                                   

EX-1

   1

                                                                       Exhibit 1

                DESCRIPTION OF COMMON STOCK AND PREFERRED STOCK

         The Company's authorized capital stock consists of 200,000,000 shares
of Common Stock, par value $.01 per share, and 20,000,000 shares of Preferred
Stock, par value $.01 per share, each of which is described below.  The summary
description of the capital stock of the Company contained herein is necessarily
general and reference should be made in each case to the Company's Restated
Articles of Incorporation and Bylaws, which are exhibits to the Registration
Statement of which this Prospectus is a part.

COMMON STOCK

         Each share of Common Stock is subject to all rights, privileges,
preferences and priorities of any class of preferred stock of the Company.
Each share of Common Stock has an equal and ratable right to receive dividends
as and when declared by the Board of Directors out of any funds of the
corporation legally available for the payment thereof.  The Company currently
has no intention to pay dividends on the shares of Common Stock in the
foreseeable future.

         In the event of a liquidation, dissolution or winding up of the
Company, the holders of Common Stock are entitled to share equally and ratably
in the assets available for distribution after payment of all liabilities,
including any liquidation preferences payable to the holders of Preferred Stock
that may at the time be outstanding.

         Each share of Common Stock is entitled to one vote in the election of
directors and on all other matters submitted to a vote of shareholders.
Holders of Common Stock have no right to cumulate their vote in the election of
directors.

         American Stock Transfer & Trust Company, 40 Wall Street, New York, New
York 10005, acts as the transfer agent and registrar of the Common Stock.

PREFERRED SHARE PURCHASE RIGHTS

         On November 8, 1996, the Board of Directors of the Company authorized
the issuance of one preferred share purchase right (a "Right") for each share
of Common Stock outstanding on November 20, 1996 and for each share of Common
Stock issued thereafter until the Distribution Date (as defined below) or the
earlier redemption or expiration of the Rights.  Each Right entitles the
registered holder to purchase from the Company one one-thousandth of a share of
Junior Participating Preferred Stock, par value $.01 per share (the "Junior
Preferred Shares"), of the Company, at a price of $56.00 per one one-thousandth
of a Junior Preferred Share (the "Purchase Price"), subject to adjustment.  The
description and terms of the Rights are set forth in a Rights Agreement (the
"Rights Agreement") dated as of November 15, 1996 between the Company and
American Stock Transfer & Trust Company, as Rights Agent (the "Rights Agent"),
and




                                      1
   2
this description of the Rights is qualified in its entirety by reference to
such agreement, which is included as an exhibit to the Registration Statement
of which this Prospectus is a part.

         Until the Distribution Date, the Rights will attach to all Common
Stock certificates representing outstanding shares and no separate Right
Certificate will be distributed.  Accordingly, a Right will be issued for each
share of Common Stock issued hereunder.  The Rights will separate from the
shares of Common Stock and a Distribution Date will occur upon the earlier of
(i) 10 business days following a public announcement that a person or group of
affiliated or associated persons (an "Acquiring Person") has acquired
beneficial ownership of 15% or more of the outstanding Voting Shares (as
defined in the Rights Agreement) of the Company, or (ii) 10 business days
following the commencement or announcement of an intention to commence a tender
offer or exchange offer the consummation of which would result in the
beneficial ownership by a person or group of 15% or more of such outstanding
Voting Shares.

         Until the Distribution Date (or earlier redemption or expiration of
the Rights) the Rights will be evidenced by the certificates representing such
Common Stock.  As soon as practicable following the Distribution Date, separate
certificates evidencing the Rights (the "Right Certificates") will be mailed to
holders of record of the shares of Common Stock as of the close of business on
the Distribution Date and such separate Right Certificates alone will
thereafter evidence the Rights.  The Rights are not exercisable until the
Distribution Date.  The Rights will expire on November 19, 2006 (the "Final
Expiration Date"), unless the Final Expiration Date is extended or the Rights
are earlier redeemed or exchanged by the Company as described below.

         If a person or group were to acquire 15% or more of the Voting Shares
of the Company, each Right then outstanding (other than Rights beneficially
owned by the Acquiring Person, which would become null and void) would become a
right to buy for the Purchase Price that number of shares of Common Stock (or
under certain circumstances, the equivalent number of one one-thousandths of a
Junior Preferred Share) that at the time of such acquisition would have a
market value of two times the Purchase Price of the Right.  If the Company were
acquired in a merger or other business combination transaction or assets
constituting more than 50% of its consolidated assets or producing more than
50% of its earning power or cash flow were sold, proper provision will be made
so that each holder of a Right will thereafter have the right to receive, upon
the exercise thereof at the then current Purchase Price of the Right, that
number of shares of Common stock of the acquiring company which at the time of
such transaction would have a market value of two times the Purchase Price of
the Right.

         The dividend and liquidation rights, and the non-redemption feature,
of the Junior Preferred Shares are designed so that the value of one
one-thousandth of a Junior Preferred Share purchasable upon exercise of each
Right will approximate the value of one Common Stock.  The Junior Preferred
Shares issuable upon exercise of the Rights will be non-redeemable and rank
junior to all other series of the Company's preferred




                                      2
   3
stock.  Each whole Junior Preferred Share will be entitled to receive a
quarterly preferential dividend in an amount per share equal to the greater of
(i) $1.00 in cash, or (ii) in the aggregate, 1,000 times the dividend declared
on the shares of Common Stock.  In the event of liquidation, the holders of the
Junior Preferred Shares will be entitled to receive a preferential liquidation
payment equal to the greater of (i) $1,000 per share, or (ii) in the aggregate,
1,000 times the payment made on the shares of Common Stock.  In the event of
any merger, consolidation or other transaction in which shares of Common Stock
are exchanged for or changed into other stock or securities, cash or other
property, each whole Junior Preferred Share will be entitled to receive 1,000
times the amount received per Common Stock.  Each whole Junior Preferred Share
will be entitled to 1,000 votes on all matters submitted to a vote of the
stockholders of the Company, and Junior Preferred Shares will generally vote
together as one class with the Common Stock and any other capital stock on all
matters submitted to a vote of shareholders of the Company.

         If required, the offer and sale of the Junior Preferred Shares
issuable upon exercise of the Rights will be registered under the Securities
Act at such time as the Rights become exercisable.

         The number of one one-thousandths of a Junior Preferred Share or other
securities or property issuable upon exercise of the Rights, and the Purchase
Price payable, are subject to customary adjustments from time to time to
prevent dilution.  The number of outstanding Rights and the number of one
one-thousandths of a Junior Preferred Share issuable upon exercise of each
Right are also subject to adjustment in the vent of a stock split of the shares
of Common Stock or a stock dividend on the shares of Common Stock payable in
shares of Common Stock or subdivisions, consolidations or combinations of the
shares of Common Stock occurring, in any such case, prior to the Distribution
Date.

         At any time after the acquisition by a person or group of affiliated
or associated persons of beneficial ownership of 15% or more of the outstanding
Voting Shares of the Company and before the acquisition by a person or group of
50% or more of the outstanding Voting Shares of the Company, the Board of
Directors may, at its option, issue shares of Common Stock in mandatory
redemption of, and in exchange for, all or part of the then outstanding and
exercisable Rights (other than Rights owned by such person or group which would
become null and void) at an exchange ratio of one share of Common Stock (or one
one-thousandth of a Junior Preferred Share) for each two shares of Common Stock
for which each Right is then exercisable, subject to adjustment.

         At any time prior to the first public announcement that a person or
group has become the beneficial owner of 15% or more of the outstanding Voting
Shares, the Board of Directors of the Company may redeem all but not less than
all the then outstanding Rights at a price of $0.01 per Right (the "Redemption
Price").  The redemption of the Rights may be made effective at such time, on
such basis and with such conditions as the Board of Directors in its sole
discretion may establish.  Immediately upon the action of the Board of
Directors ordering redemption of the Rights, the right to exercise the Rights




                                      3
   4
will terminate and the only right of the holders of Rights will be to receive
the Redemption Price.

         Until a Right is exercised, the holder thereof, as such, will have no
rights as a shareholder of the Company, including, without limitation, the
right to vote or to receive dividends.

         The terms of the Rights may be amended by the Board of Directors of
the Company without the consent of the holders of the Rights, including an
amendment to extend the Final Expiration Date, and, provided a Distribution
Date has not occurred, to extend the period during which the Rights may be
redeemed, except that after the first public announcement that a person or
group has become the beneficial owner of 15% or more of the outstanding Voting
Shares, no such amendment may materially and adversely affect the interests of
the holders of the Rights.

         The Rights have certain anti-takeover effects.  The Rights will cause
substantial dilution to a person or group that attempts to acquire the Company
on terms not determined by the Board of Directors to be in the best interests
of all shareholders.  The Rights will not interfere with a merger or other
business combination approved by the Board of Directors, prior to the time that
a person or group has acquired beneficial ownership of 15% or more of the
Common Stock, since the Rights may be redeemed by the Company prior to that
time.




                                      4