UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

Amendment No. 1

For the quarterly period ended June 30, 2011

For the transition period from                          to                         

Commission File Number 000-29187-87

CARRIZO OIL & GAS, INC.

(Exact name of registrant as specified in its charter)

(713) 328-1000

(Registrant’s telephone number)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports) and (2) has been subject to such filing requirements for the past 90 days.

YES  x    NO  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).

YES  x    NO  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).

YES  ¨    NO  x

The number of shares outstanding of the registrant’s common stock, par value $0.01 per share, as of July 29, 2011 was 39,297,781.

Explanatory Note

The sole purpose of this amendment to our Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2011, originally filed with the Securities and Exchange Commission on August 9, 2011, is to furnish Exhibit 101 to the Form 10-Q which contains the XBRL (eXtensible Business Reporting Language) Interactive Data File for the financial statements and notes included in Part 1, Item 1 of the Form 10-Q. As permitted by Rule 405(a) (2)(ii) of Regulation S-T, Exhibit 101 was required to be furnished by amendment within 30 days of the original filing date of the Form 10-Q.

No changes have been made to the Form 10-Q other than the furnishing of Exhibit 101 described above. This amendment does not reflect subsequent events occurring after the original filing date of the Form 10-Q or modify or update in any way disclosures made in the Form 10-Q.

Pursuant to rule 406T of Regulation S-T, the Interactive Data File on Exhibit 101 hereto are deemed not filed or part of a registration statement or prospectus for purposes of Section 11 or 12 of the Securities Act of 1933, as amended, are deemed not filed for purposes of Section 18 of the Securities Act of 1934, as amended, and otherwise are not subject to liability under those sections.

Item 6. Exhibits.

The following exhibits are required by Item 601 of Regulation S-K and are filed as part of this report:

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the Registrant has duly caused this Report to be signed on its behalf by the undersigned, thereunto duly authorized.