CABOT CORP — Director's Dealing 2005

Dec 23, 2005

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: CABOT CORP (CBT)
CIK: 0000016040
Period of Report: 2005-12-20

Reporting Person: SPO ADVISORY CORP (10% Owner)
Reporting Person: WILLIAM ERNST OBERNDORF TRUST (10% Owner)
Reporting Person: OBERNDORF FAMILY PARTNERS (10% Owner)
Reporting Person: OBERNDORF WILLIAM E (10% Owner)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2005-12-20	Common Stock	P	600	$35.32	Acquired	600	Indirect
2005-12-20	Common Stock	P	100	$35.34	Acquired	700	Indirect
2005-12-20	Common Stock	P	1000	$35.35	Acquired	1700	Indirect
2005-12-20	Common Stock	P	1400	$35.36	Acquired	3100	Indirect
2005-12-20	Common Stock	P	3000	$35.37	Acquired	6100	Indirect
2005-12-20	Common Stock	P	200	$35.38	Acquired	6300	Indirect
2005-12-20	Common Stock	P	500	$35.39	Acquired	6800	Indirect
2005-12-20	Common Stock	P	3900	$35.40	Acquired	10700	Indirect
2005-12-20	Common Stock	P	14400	$35.41	Acquired	25100	Indirect
2005-12-20	Common Stock	P	300	$35.42	Acquired	25400	Indirect
2005-12-20	Common Stock	P	6100	$35.45	Acquired	31500	Indirect
2005-12-20	Common Stock	P	3600	$35.46	Acquired	35100	Indirect
2005-12-20	Common Stock	P	1500	$35.47	Acquired	36600	Indirect
2005-12-20	Common Stock	P	4600	$35.48	Acquired	41200	Indirect
2005-12-20	Common Stock	P	8300	$35.49	Acquired	49500	Indirect
2005-12-20	Common Stock	P	50500	$35.50	Acquired	100000	Indirect
2005-12-21	Common Stock	P	200	$35.47	Acquired	100200	Indirect
2005-12-21	Common Stock	P	50	$35.48	Acquired	100250	Indirect
2005-12-21	Common Stock	P	150	$35.49	Acquired	100400	Indirect
2005-12-21	Common Stock	P	42650	$35.50	Acquired	143050	Indirect
2005-12-21	Common Stock	P	200	$35.47	Acquired	143250	Indirect
2005-12-21	Common Stock	P	50	$35.48	Acquired	143300	Indirect
2005-12-21	Common Stock	P	150	$35.49	Acquired	143450	Indirect
2005-12-21	Common Stock	P	42650	$35.50	Acquired	186100	Indirect

Footnotes

F1: 7,648,600 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"), William E. Oberndorf ("WEO") and William J. Patterson ("WJP"), the three controlling persons of SPO Corp. 309,400 shares of the issuer's common stock are owned directly by San Francisco Partners II, 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.

F2: Additionally, (i) 143,050 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"), and (ii) 43,050 shares may be deemed to be indirectly beneficially owned by WEO solely in his capacity as trustee for the Oberndorf Trust, the sole general partner of Oberndorf Family Partners, a family partnership.