Amendment to Warrant Agreement among HMP Equity Holdings Corporation, Huntsman Holdings, Huntsman Group Inc., and Wells Fargo Bank

Exhibit 4.66

AMENDMENT
TO
WARRANT AGREEMENT

        This AMENDMENT to the WARRANT AGREEMENT (the "Warrant Agreement") dated as of May 9, 2003 between HMP EQUITY HOLDINGS CORPORATION, a Delaware corporation (the "Company"), HUNTSMAN HOLDINGS, LLC, a Delaware limited liability company ("Huntsman Holdings"), HUNTSMAN GROUP INC., a Delaware corporation and WELLS FARGO BANK, NATIONAL ASSOCIATION, a national banking association, (as successor by merger to Wells Fargo Bank Minnesota, National Association), organized under the laws of the United States of America, as Warrant Agent (the "Amendment") is made and entered into as of January 20, 2005 by and between each of the parties to the Warrant Agreement.

A.

Huntsman Corporation, a Delaware corporation and a subsidiary of Huntsman Holdings is contemplating a Qualifying IPO and upon completion of its proposed merger with Huntsman Holdings will be the successor to Huntsman Holdings.



B.

The Warrant Agreement provides that Parent may exercise a Mandatory Exchange Right in connection with a Qualifying IPO, requiring all Holders of Warrants and Warrant Shares to sell to Parent all such Warrants and Warrant Shares in exchange for Parent Equity Securities.



C.

Although this Amendment does not constitute a Mandatory Exchange Notice, Huntsman Holdings and the Company desire to clarify certain provisions of the Warrant Agreement prior to exercise of the Mandatory Exchange Right which exercise will only occur after written notice thereof is provided by Huntsman Holdings.



D.

Section 20 of the Warrant Agreement authorizes the amendment of the Warrant Agreement upon the written consent of the Holders of a majority of the outstanding Warrants (excluding Warrants held by the Company or any of its Affiliates).



E.

Holders of a majority of the outstanding Warrants (excluding Warrants held by the Company or any of its Affiliates) have consented in writing to this Amendment as evidenced by their execution hereof.

        NOW, THEREFORE, in consideration of the premises and mutual agreements herein, the Company, Huntsman Holdings, Huntsman Group, Inc. and the Warrant Agent hereby agree as follows:

        SECTION 1.     Amendments.    

(a)

Section 16(c) is hereby amended in its entirety to read as follows:



(c)

If an Exchange Request is made in connection with a Qualifying IPO or if Parent exercises its Mandatory Exchange Right in connection with a Qualifying IPO, then Parent shall register under the Securities Act the resale of Parent Equity Securities issued in connection with such Exchange Request or exercise of the Mandatory Exchange Right in accordance with the Registration Rights Agreement; provided that the right of all such recipients to receive Parent Equity Securities will be conditioned upon such Holder agreeing to a lock-up on the sale or other disposition of such Parent Equity Securities for the period commencing from the consummation of the Qualifying IPO and ending on the earlier of (1) the date required by the managing underwriter of the Qualifying IPO for holders of shares of Parent generally, not to exceed the date that is 180 days following the effective date of such registration, and (2) the first date that any holders of Parent Equity Securities are generally able to sell their shares.

(b)

The following definitions are hereby added to the definitions included in the Agreement:

        "Admat Preferred Unit Liquidation Value" means the liquidation value of the Admat Preferred Units pursuant to their terms which is $513,250,000.

        "IPO Price" shall be equal to the price to the public per share shown on the cover of the final prospectus relating to the Qualifying IPO.

        "Total Outstanding Parent Equity Securities" means the total number of outstanding shares of common stock of Parent as disclosed in the final prospectus relating to the Qualifying IPO, including without limitation all shares sold in the IPO and all shares to be issued in exchange for Warrants and Warrant Shares.

        "Total Warrant Shares" shall mean the total number of shares of Common Stock that have been issued upon the exercise of Warrants and that remain issuable upon the exercise of the unexercised Warrants (excluding Warrants held by the Company or any of its Affiliates).

(c)

The following definitions contained in the Warrant Agreement are hereby amended in their entirety to read as follows:

        "Fair Value of Parent Equity Securities" means (i) in connection with any Exchange Request or exercise of Mandatory Exchange Right the notice of either of which is given prior to or within five business days after the consummation of a Qualifying IPO, the IPO Price, (ii) in connection with any Exchange Request or exercise of Mandatory Exchange Right the notice of either of which is given five business days or more after consummation of a Qualifying IPO the average of the closing sales prices of such securities on the primary exchange on which such shares are traded for each of the five trading days preceding such determination or (iii) in all other circumstances, the fair value of the Parent Equity Securities as agreed by Huntsman Holdings and the Holders of a majority of the outstanding Warrant Shares on a fully diluted basis or, absent such agreement, as determined by an Independent Financial Expert mutually acceptable to Huntsman Holdings and the Holders of a majority of the outstanding Warrant Shares on a fully diluted basis.

        "Fair Value of Warrant Shares" means (A) the product of (i) sum of (x) Fair Value of Parent Equity Securities multiplied by the Total Outstanding Parent Equity Securities minus (y) the IPO Price multiplied by the Total Outstanding Parent Equity Securities sold in the Qualifying IPO by Parent minus (z) the AdMat Preferred Liquidation Value, multiplied by (ii) the Total Warrant Shares divided by the sum of the number of shares of Common Stock outstanding and the number of shares that remain issuable upon the exercise of unexercised Warrants, divided by (B) the Total Warrant Shares. If any unexercised Warrants are being exchanged for Parent Equity Securities, then the Fair Value of Warrant Shares shall be net of the Exercise Price for such unexercised Warrants.

        SECTION 2.     Miscellaneous Provisions.    

(a)

This Amendment is limited solely for the purposes and to the extent expressly set forth herein and, except as expressly modified hereby, the terms, provisions and conditions of the Warrant Agreement shall continue in full force and effect and are hereby ratified and confirmed in all respects. In the event of any conflict between the terms of this Amendment and the terms of the Warrant Agreement, the terms of this Amendment shall govern. This Amendment shall be effective as of the date first written above.



(b)

The invalidity or unenforceability of any provision of this Amendment shall not in any manner or way affect any other provision hereof, and this Amendment shall be construed, if possible, as if amended to conform to legal requirements, failing which it shall be construed as if any such offending provision were omitted.

2

(c)

Whenever the Warrant Agreement is referred to in the Warrant Agreement or in any other agreement, documents and instruments, such reference shall be deemed to be to the Warrant Agreement, as amended by this Amendment. The Warrant Agreement, as amended by this Amendment, constitutes the entire understanding of the parties hereto with respect to the subject matter hereof.



(d)

This Amendment may be executed in any number of counterparts and each of such counterparts shall for all purposes be deemed to be an original, and all such counterparts shall together constitute but one and the same agreement.



(e)

This Amendment shall be deemed to be a contract made under the laws of the State of New York and shall be governed and construed in accordance with the laws of said State, without regard to the conflict of law rules thereof.

3

        IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed, as of the day and year first above written.

4

        Each of the holders of Warrants or Warrant Shares who has executed this Amendment below has done so solely to evidence its consent to this Amendment pursuant to Section 20 of the Warrant Agreement and to represent and warrant that it is the beneficial owner of the number of Warrants set forth opposite its name

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

QuickLinks