UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                                   FORM 8-A/A
                         POST-EFFECTIVE AMENDMENT NO. 1


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

                             ATWOOD OCEANICS, INC.
             (Exact Name of Registrant as Specified in Its Charter)



                      TEXAS                      74-1611874
           (State of Incorporation            (I.R.S. Employer
               or Organization)            Identification Number)


            15835 Park Ten Place Drive
                     Houston, Texas                       77084
         (Address of Principal Executive Offices)       (Zip Code)

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
Instruction 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 Act registration statement file number to which this form relates:
001-13167.

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

   Title of Each Class                       Name of Each Exchange on Which
   To Be So Registered                       Each Class is to be Registered
   -------------------                       ---------------------------------

   Preferred Stock Purchase Rights           New York Stock Exchange

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

                                      None
                                (Title of Class)



         The undersigned registrant hereby amends the Registration Statement on
Form 8-A filed by the registrant with the Securities and Exchange Commission on
October 21, 2002, as set forth below:

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

         On September 12, 2002, the Board of Directors of Atwood Oceanics, Inc.
(the "Company"), authorized and declared a dividend of one Right (a "Right")
for each outstanding share of Common Stock, par value $1.00 per share ("Common
Stock"), of the Company (the "Common Shares"). The dividend was payable on
November 5, 2002 (the "Record Date") to the shareholders of record of the
Common Shares at the close of business on that date. The description and terms
of the Rights are set forth in a Rights Agreement (the "Rights Agreement")
between the Company and Continental Stock Transfer & Trust Company, as Rights
Agent (the "Rights Agent"), dated as of October 18, 2002. Capitalized terms
used and not defined herein have the meanings given to them in the Rights
Agreement.

         On March 2, 2006, the Company announced that its Board of Directors
had approved a two-for-one stock split of its Common Stock (the "Stock Split")
to be effected in the form of a 100% stock dividend payable April 7, 2006 (the
"Split Date"), on all Common Shares outstanding as of the close of business on
March 24, 2006 (the "Record Date"). There were 15,451,586 Common Shares
outstanding on the Record Date. Prior to the Stock Split, upon the occurrence
of certain events, each Right entitles the holder to purchase from the Company
one one-thousandth of a share of Series A Junior Participating Preferred Stock,
no par value, of the Company (the "Preferred Shares"), at a price of $150.00
per one one-thousandth of a Preferred Share. In connection with the Stock
Split, pursuant to Section 11(n) of the Rights Agreement, effective upon the
Split Date, the number of the Preferred Shares purchasable upon the exercise of
each Right will be decreased from one one-thousandth of a Preferred Share to
one two-thousandth of a Preferred Share, and the number of outstanding Rights
will be increased by 100%, such that each Common Share outstanding immediately
after the Stock Split shall have issued with respect to it one Right. In
addition, pursuant to Section 23(a) of the Rights Agreement, the Redemption
Price of each Right will be decreased by one-half from $0.01 to $0.005 upon the
Split Date.

         A copy of the Certificate of Adjustment delivered on March 17, 2006 by
the Company to the Rights Agent and a form of the letter to be sent to the
Company's shareholders on or about the Split Date in connection with the Stock
Split and providing notice of adjustment to the Rights, each required pursuant
to the terms of the Rights Agreement, are attached as Exhibits 4.1 and 99.1,
respectively, to this Amendment No. 1 and are incorporated herein by reference.

The following Summary of Rights to Purchase Preferred Shares reflects
adjustments made in connection with the Stock Split.

         Until the earlier to occur of (i) 10 days following a public
announcement that a person or group of affiliated or associated persons (an
"Acquiring Person") has acquired beneficial ownership of 15 percent or more of
the outstanding Common Shares and (ii) 10 business days (or such later date as
may be determined by action of the Board of Directors of the Company prior to

such time as any person or group of affiliated or associated persons becomes an
Acquiring Person) following the commencement of, or first public 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
affiliated or associated persons of 15 percent or more of the outstanding
Common Shares (the earlier of such dates being herein referred to as the
"Distribution Date"), the Rights will be evidenced, with respect to any of the
Common Share certificates outstanding as of the Record Date, by such Common
Share certificate with a copy of a Summary of Rights to Purchase Preferred
Shares ("Summary of Rights") in substantially the form attached as Exhibit C to
the Rights Agreement. The Rights Agreement provides that an Acquiring Person
shall not include any existing shareholder owning 15 percent or more of the
Company's Common Shares as of the Record Date unless such shareholder acquires
an additional 5 percent more of the Company's Common Shares than it owned as of
the Record Date.

         The Rights Agreement provides that, until the Distribution Date (or
earlier redemption or expiration of the Rights), the Rights will be transferred
with and only with the Common Shares. Until the Distribution Date (or earlier
redemption or expiration of the Rights), new Common Share certificates issued
after the Record Date, upon transfer or new issuance of Common Shares, will
contain a notation incorporating the Rights Agreement by reference. Until the
Distribution Date (or earlier redemption or expiration of the Rights), the
surrender for transfer of any certificates for Common Shares outstanding on or
after the Record Date, even without such notation or a copy of this Summary of
Rights being attached thereto, will also constitute the transfer of the Rights
associated with the Common Shares represented by such certificate. As soon as
practicable following the Distribution Date, separate certificates evidencing
the Rights ("Right Certificates") will be mailed to holders of record of the
Common Shares as of the close of business on the Distribution Date and such
separate Right Certificates alone will evidence the Rights.

         The Rights are not exercisable until the Distribution Date. The Rights
will expire on November 5, 2012 (the "Final Expiration Date"), unless the Final
Expiration Date is extended or unless the Rights are earlier redeemed or
exchanged by the Company, in each case, as described below.

         The Purchase Price payable, and the number of Preferred Shares or
other securities or property issuable, upon exercise of the Rights are subject
to adjustment from time to time to prevent dilution (i) in the event of a stock
dividend on, or a subdivision, combination or reclassification of, the
Preferred Shares, (ii) upon the grant to holders of the Preferred Shares of
certain rights or warrants to subscribe for or purchase Preferred Shares at a
price, or securities convertible into Preferred Shares with a conversion price,
less than the then current market price of the Preferred Shares or (iii) upon
the distribution to holders of the Preferred Shares of evidences of
indebtedness or assets (excluding regular periodic cash dividends paid out of
earnings or retained earnings or dividends payable in Preferred Shares) or of
subscription rights or warrants (other than those referred to above).

         The number of outstanding Rights and the number of one two-thousandths
of a Preferred Share issuable upon exercise of each Right are also subject to
adjustment in the event of a stock

split of the Common Shares or a stock dividend on the Common Shares payable in
Common Shares or subdivisions, consolidations or combinations of the Common
Shares occurring, in any such case, prior to the Distribution Date.

         Preferred Shares purchasable upon exercise of the Rights will not be
subject to redemption by the Company. The Preferred Shares shall be entitled to
an aggregate dividend of 2000 multiplied times the dividend declared per Common
Share. If no dividend is declared in a quarter, the Preferred Shares are
entitled to a minimum preferential quarterly dividend of $0.01 per share. In
the event of liquidation, the holder of the Preferred Shares will be entitled
to the greater of a minimum preferential liquidation payment of $1.00 per share
and an aggregate payment of 2000 multiplied times the payment made per Common
Share. Each Preferred Share will have 2000 votes, voting together with the
Common Shares. Finally, in the event of any merger, consolidation or other
transaction in which Common Shares are exchanged, each Preferred Share will be
entitled to receive 2000 multiplied times the amount received per Common Share.
These rights are protected by customary antidilution provisions.

         Because of the nature of the Preferred Shares' dividend, liquidation
and voting rights, the value of the one two-thousandth interest in a Preferred
Share purchasable upon exercise of each Right should approximate the value of
one Common Share.

         In the event that the Company is acquired in a merger or other
business combination transaction or 50 percent or more of its consolidated
assets or earning power are sold after a person or group of affiliated or
associated persons has become an Acquiring Person, 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 exercise price of the Right, that
number of shares of common stock of the acquiring company which at the time of
such transaction will have a market value of two times the exercise price of
the Right. In the event that any person or group of affiliated or associated
persons becomes an Acquiring Person, proper provision shall be made so that
each holder of a Right, other than Rights beneficially owned by the Acquiring
Person (which will thereafter be null and void and nontransferable), will
thereafter have the right to receive upon exercise that number of Common Shares
of the Company having a market value of two times the exercise price of the
Right.

         At any time after any person or group of affiliated or associated
persons becomes an Acquiring Person and prior to the acquisition by such person
or group of 50 percent or more of the outstanding Common Shares, the Board of
Directors of the Company may exchange the Rights (other than Rights owned by
such person or group which will have become null and void and nontransferable),
in whole or in part, at an exchange ratio of one Common Share, or one
two-thousandth of a Preferred Share (or of a share of a class or series of the
Company's preferred stock having equivalent rights, preferences and
privileges), per Right (subject to adjustment).

         With certain exceptions, no adjustment in the Purchase Price will be
required until cumulative adjustments require an adjustment of at least one
percent in such Purchase Price. The Company may, but shall not be required to,
issue fractions of a Preferred Share (other than one two-thousandth of a
Preferred Share or any integral multiple thereof, which may, at the election of
the Company, be evidenced by depositary receipts) and in lieu thereof, an
adjustment in cash

will be made based on the market price of the Preferred Shares on the last
trading day prior to the date of exercise.

         At any time prior to the close of business on the tenth day following
a public announcement that an Acquiring Person has become such an Acquiring
Person, the Board of Directors of the Company may redeem the Rights in whole,
but not in part, at a price of $.005 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. The time at which the Rights are redeemed by the Company is herein
referred to as the "Redemption Date." Immediately upon any redemption of the
Rights, the right to exercise the Rights will terminate and the only right
thereafter of the holders of Rights will be to receive the Redemption Price.

         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 without
limitation an amendment to lower certain thresholds described above to not less
than the greater of (i) the sum of 0.001 percent and the largest percentage of
the outstanding Common Shares then known by the Company to be beneficially
owned by any person or group of affiliated or associated persons and (ii) 10
percent, except that from and after such time as any person or group of
affiliated or associated persons becomes an Acquiring Person no such amendment
may adversely affect the interests of the holders of the Rights.

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

         The Preferred Shares shall rank, with respect to the payment of
dividends and as to distributions of assets upon liquidation, dissolution or
winding up of the Company, junior to all other series of preferred stock of the
Company, if any, unless the Board of Directors of the Company shall
specifically determine otherwise in fixing the powers, preferences and
relative, participating, optional and other special rights of the shares of any
such other series and the qualifications, limitations and restrictions thereof.

         As of March 24, 2006, there were 15,451,586 Common Shares issued and
outstanding, and an aggregate of an additional 1,282,665 Common Shares reserved
for issuance under the Company's stock incentive plans and related agreements.
One Right will be distributed with each Common Share issued in connection with
the Stock Split, which will be equal to the number of Common Shares owned of
record at the close of business on the Record Date. One Right will continue to
be issued with respect to each Common Share that shall become outstanding
between the Record Date and the earliest of the Distribution Date, the
Redemption Date and the Final Expiration Date. In certain circumstances, the
Company may issue Rights with respect to Common Shares issued following the
Distribution Date and prior to the earlier of the Redemption Date and the Final
Expiration Date. The Company's Board of Directors has initially reserved
500,000 Preferred Shares for issuance upon exercise of the Rights, which number
is subject to adjustment from time to time in accordance with the Rights
Agreement.

         The Rights have certain anti-takeover effects. The Rights will cause
substantial dilution to a person or group that attempts to acquire the Company
in a manner or on terms not approved by the Board of Directors. The Rights,
however, should not deter any prospective offeror willing to negotiate in good
faith with the Board of Directors, nor should the Rights interfere with any
merger or business combination approved by the Board of Directors of the
Company prior to an Acquiring Person's acquiring 15 percent or more of the
Common Shares.

         The Amended and Restated Certificate of Formation (as amended from
time to time, the "Certificate of Formation") and the Amended and Restated
By-Laws (the "By-Laws") of the Company contain several provisions that may make
the acquisition of control of the Company by means of a tender offer, open
market purchases, proxy fight or otherwise more difficult. These provisions are
expected to discourage certain types of transactions that may involve an actual
or threatened change of control of the Company and to encourage persons seeking
to acquire control of the Company to consult first with the Company's Board to
negotiate the terms of any proposed business combination or offer. Takeovers or
changes in the Board that might be proposed and effected without prior
consultation and negotiation with the Board or the Company's management would
not necessarily be detrimental to the Company and its shareholders. However,
the Company nonetheless believes that the benefits of increased protection of
the Company's potential ability to negotiate with the proponent of an
unfriendly or unsolicited proposal to take over or restructure the Company
outweigh the disadvantages of discouraging such proposal, because, among other
things, negotiation of such proposals could result in an improvement of their
terms.

         The Company has in place certain additional measures which could also
be considered to have anti-takeover effects. The Company's Certificate of
Formation and By-Laws (i) provide that the size of the Board will be fixed by
resolution of the directors of the Company, (ii) provide that directors may be
removed only with the approval of the holders of at least two-thirds of the
combined voting power of the outstanding shares of the Company capital stock
entitled to vote generally in the election of directors (the "Voting Stock"),
(iii) provide that any vacancy on the Board may be filled by the remaining
directors then in office, though less than a quorum, and (iv) authorize the
Board to issue one or more series of preferred stock and to determine with
respect to any such series the terms and rights thereof.

         The foregoing is a summary of certain provisions in the Company's
Certificate of Formation and By-Laws, and is qualified in its entirety by
reference to the Certificate of Formation and By-Laws.

         A copy of the Rights Agreement between the Company and the Rights
Agent specifying the terms of the Rights, except for adjustments made in
connection with the Stock Split, is filed as Exhibit 4.2 hereto and is
incorporated herein by reference. The foregoing description of the Rights does
not purport to be complete and is qualified in its entirety by reference to the
Rights Agreement, except for the adjustments relating to the Stock Split which
are discussed herein.

ITEM 2.           EXHIBITS

          4.1  Certificate of Adjustment dated as of March 17, 2006 delivered
               pursuant to the Rights Agreement by and between the Company and
               Continental Stock Transfer & Trust Company (Incorporated by
               reference to Exhibit 4.1 to the Registrant's Current Report on
               Form 8-K, filed March 23, 2006).

          4.2  Rights Agreement, dated effective October 18, 2002, between
               Atwood Oceanics, Inc. and Continental Stock Transfer & Trust
               Company, which includes as Exhibit B thereto the Form of Right
               Certificate. (Incorporated by reference from Exhibit 4.1 to Form
               8-A filed October 21, 2002).

          99.1 Proposed Letter from John R. Irwin, President of the Company, to
               shareholders of the Company.

                                   SIGNATURES

         Pursuant to the requirements of Section 12 of the Securities Exchange
Act of 1934, as amended, the registrant has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereto duly
authorized.


                                             ATWOOD OCEANICS, INC.


Dated:   April 5, 2006              By:      /s/ James M. Holland
                                       ----------------------------------------
                                                    James M. Holland
                                                    Senior Vice President


                               INDEX TO EXHIBITS

Exhibit          Description

          4.1  Certificate of Adjustment dated as of March 17, 2006 delivered
               pursuant to the Rights Agreement by and between the Company and
               Continental Stock Transfer & Trust Company (Incorporated by
               reference to Exhibit 4.1 to the Registrant's Current Report on
               Form 8-K, filed March 23, 2006).

          4.2  Rights Agreement, dated effective October 18, 2002, between
               Atwood Oceanics, Inc. and Continental Stock Transfer & Trust
               Company, which includes as Exhibit B thereto the Form of Right
               Certificate. (Incorporated by reference from Exhibit 4.1 to Form
               8-A filed October 21, 2002).

          99.1 Proposed Letter from John R. Irwin, President of the Company, to
               shareholders of the Company.