Six Democrat senators asked the Department of Justice to investigate possible market manipulation by oil refineries on the west coast as the cause of spikes in gasoline prices in May and October. Gas prices hit a record high of $5.

 "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 wrote.

At the time, refineries published reports of maintenance shutdowns. The senators want the DOJ to examine every single refinery to establish if this is true. Independent energy consultant Robert McCullough found that two refineries continued to work through these shutdowns.

California is cut off from pipelines and refinery networks, which can lead to supply and price problems. A fire shut down Chevron’s plant in Richmond, and a power failure in a Los Angeles refinery led to problems for Exxon Mobile.

Valero’s spokesman Bill Day said these challenges, plus California being cut off, lead to price spikes, claiming an investigation would come up empty.

"The self-inflicted factors that contributed to the temporary price increase in California remain in place," Day said. "You don't need a federal investigation to figure that out."

All six senators are from the west coast: Dianne Feinstein and Barbara Boxer from California, Rony Wyden and Jeff Merkley of Oregon, and Maria Cantwell and Patty Murray of Washington.

The DOJ said they will respond accordingly.