NEW YORK (Standard&Poor's) May 9, 2005--Standard&Poor's Ratings Services said today that it lowered its corporate credit rating on Calpine Corp. and its subsidiaries to 'B-' from 'B'. The outlook is negative. In addition, Standard&Poor's lowered its ratings on debt that Calpine guarantees. The ratings for the following debt issues remain unchanged: the 'BBB-' SPUR rating on Gilroy Energy Center LLC's bonds, the 'BB-' rating on the Rocky Mountain Energy Center LLC and the Riverside Energy Center LLC loans, the 'CCC+' rating on the third lien Calpine Generating Co. LLC debt, and the 'BBB' rating on Power Contract Financing LLC's bonds. The San Jose, Calif.-based company, which develops, acquires, owns, and operates power generation facilities,