Wyden said he was curious why U.S. consumers paid record-high prices at the pump at the same time that domestic oil production was also at a record high.
"This most recent round of gas price increases has come at a time of year when gas prices are typically at their lowest point but that has not been the case this autumn and winter," Wyden wrote.
Most regions of the United States saw seasonal spikes for gasoline earlier than average this year. Last month, the EIA said refinery outages and the switch to more expensive summer blends of gasoline were in part to blame for higher prices at the pump.
So-called crack spreads, the difference between wholesale gasoline prices and crude oil prices, were identified by the EIA as accounting for more than 60 percent of the price increase.
Prices started to fall by March, however. Motor group AAA reports a national average price for a gallon of regular unleaded gasoline at $3.70, about 3 cents lower than last week.
The EIA said it expects gasoline prices for 2013 to average $3.55 per gallon.
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