Tesoro Corporation's Eagle Refinery in unincorporated Contra Costa County ranked fourth for releasing 1.8 million pounds of chemicals.
Valero's Benicia refinery ranked fifth for releasing 1.7 million pounds of toxic waste.
Chevron's Richmond refinery was ninth with 1.2 million pounds.
The top offender was Chemical Waste Management in Kings County which dumped 8.8 million pounds of chemicals in 2006.