While the national average for a gallon of gas has dropped nearly 20 cents since peaking in early April, prices on the West Coast of the U.S. recently began rising again, even as prices in every other region of the country trend downwards.

For the week ending May 14, the U.S. Energy Information Administration had the national average at $3.814/gallon. But on the West Coast, that price had gone up to $4.308/gallon, up $.137/gallon from just two weeks earlier.

Even when you subtract California from the equation, the average West Coast gas price is still $4.11/gallon, an increase of $.052/gallon over the previous two weeks.

Los Angeles and San Francisco both surpass the California average of $4.414/gallon with prices of $4.489 and $4.433 per gallon, respectively.

Compare that to Cleveland ($3.697/gallon) and Houston ($3.713/gallon).

A rep for the AAA calls it a “a tale of two coasts,” but the graph above shows that the only other region whose prices haven’t matched the national average is the Rocky Mountain region, where prices have generally maintained the same level during the last several weeks.

So what’s the problem?

According to USA Today, analysts say it’s not increased demand and instead point the blame at a refinery slowdown in the western part of the country.

A rep for Western States Petroleum Association tells the paper that unexpected maintenance at refineries is partly to blame and “If they are patient… the decline in crude oil price we’re seeing … should translate to lower prices at the pump.”

But a gasoline analyst at Utility Consumers’ Action Network in San Diego tells USA Today that there is a problem with lack of competition among refineries in the area: “We’re not saying there’s a conspiracy. It’s just that with this few competitors, it’s very easy to game prices by turning off capacity.”

UPDATE: Consumerist reader Victor points out that Congressman Peter DeFazio has asked the Justice Department’s Oil and Gas Price Fraud Working Group to look into the timing of the “maintenance” slowdowns at a number of West Coast refineries.

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