TENTH AMENDMENT TO THE PREMCOR RETIREMENT SAVINGS PLAN

Exhibit 10.3

TENTH AMENDMENT TO THE

PREMCOR RETIREMENT SAVINGS PLAN

WHEREAS, The Premcor Refining Group Inc. (“Company”) previously adopted the Premcor Retirement Savings Plan (“Plan”); and

WHEREAS, the Company reserved the right to amend the Plan pursuant to Section 16.1 thereof; and

WHEREAS, the Company desires to amend the Plan to reduce the limit for certain mandatory distributions, effective March 28, 2005;

NOW, THEREFORE, effective March 28, 2005, the Plan is amended as follows:

All references to the amount “$5,000” in Sections 9, 10, 17.11(a) and 17.20 are hereby replaced by the amount “$1,000”.

IN WITNESS WHEREOF, the Company has executed this amendment as of this 14 day of February, 2005.