UPDATE 1-Chevron Richmond refinery HCU malfunctions -sources

(Adds Chevron no comment, details)

HOUSTON, July 10 (Reuters) - A hydrocracking unit at Chevron Corp's (CVX.N) 245,271-barrel-per-day Richmond, California, refinery malfunctioned on Friday, according to sources familiar with refinery operations.

Wholesale gasoline prices in San Francisco and Los Angeles spiked when Chevron was seen heavily buying replacement gasoline for the San Francisco Bay area refinery on Friday morning, the sources said.

Wholesale gasoline prices climbed 5.75 cents over August NYMEX RBOB contracts on Friday in Los Angeles while San Francisco Bay prices shot up 10.75 cents, traders said.

A Chevron spokesman declined to discuss refinery operations.

In the Los Angeles market, gasoline blended to meet California's strict environmental standards sold as high as 13.75 cents over the August NYMEX RBOB contract while in San Francisco gasoline sold as high as 17.75 cents over the August NYMEX RBOB.

Chevron was also in the process of taking down a reformer and diesel hydrotreater for two weeks of planned work at the Richmond refinery, sources familiar with refinery operations have told Reuters. (Reporting by Erwin Seba; Editing by Christian Wiessner)