WASHINGTON (Reuters) - Six U.S. senators on Tuesday called for the U.S. Justice Department to investigate whether market manipulation by West Coast oil refiners contributed to a price spike in May and October that sent gasoline prices to record highs above $5 a gallon.

The senators, all Democrats, want the Justice Department to conduct a "refinery-by-refinery probe" and subpoena records from California refineries to see whether public reports of maintenance shutdowns were accurate. Two of the state's largest refiners are Valero Energy Corp and Tesoro Corp.

"We are requesting a Department of Justice investigation of possible market manipulation and false reporting by oil refineries, which may have created a perception of a supply shortage when in fact refineries were still producing," the senators said in a letter to U.S. Attorney General Eric Holder.

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