CABOT CORP — Director's Dealing 2007

May 2, 2007

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: CABOT CORP (CBT)
CIK: 0000016040
Period of Report: 2007-04-27

Reporting Person: SPO ADVISORY CORP (10% Owner)
Reporting Person: OBERNDORF WILLIAM E (10% Owner)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2007-04-27	Common Stock	P	74700	$46.00	Acquired	9587550	Indirect
2007-04-30	Common Stock	P	24000	$45.9450	Acquired	9611550	Indirect
2007-04-30	Common Stock	P	10300	$45.3000	Acquired	9621850	Indirect

Footnotes

F1: The individual acquiring these shares is William E. Oberndorf ( WEO ), for his self-directed individual retirement account. Additionally, (i) 333,650 shares of the issuer's common stock may be deemed to be indirectly beneficially owned by WEO solely in his capacity as a trustee for the William and Susan Oberndorf Trust, dated 10/15/98 ("Oberndorf Trust"), (ii) 100,000 shares may be deemed to be indirectly beneficially owned by WEO solely in his capacity as general partner of Oberndorf Family Partners, a California limited partnership, and (iii) 10,000 shares may be deemed to be indirectly beneficially owned by WEO solely in his capacity as trustee for the accounts of his two children, Peter C. Oberndorf & William Ernst Oberndorf.

F2: Additionally, 8,648,600 shares of the issuer's common stock are owned directly by SPO Partners II, L.P. ("SPO Partners"), and may be deemed to be indirectly beneficially owned by (i) SPO Advisory Partners, L.P. ("SPO Advisory"), the sole general partner of SPO Partners, (ii) SPO Advisory Corp. ("SPO Corp."), the sole general partner of SPO Advisory, and (iii) John H. Scully ("JHS"), WEO and William J. Patterson ("WJP"), the three controlling persons of SPO Corp. 415,600 shares of the issuer's common stock are owned directly by San Francisco Partners, L.P. ("SF Partners"), and may be deemed to be indirectly beneficially owned by (i) SF Advisory Partners, L.P. ("SF Advisory"), the sole general partner of SF Partners, (ii) SPO Corp., the sole general partner of SF Advisory, and (iii) JHS, WEO and WJP, the three controlling persons of SPO Corp.

F3: Additionally, 5,000 shares of the issuer's common stock are owned directly by Betty Jane Weimer