President Bush has ordered an investigation into possible cheating in the fuel markets.
During the last few days, Mr Bush, under pressure to do something about fuel prices that are expected to stay high through the summer,
asked his Energy and Justice departments to open inquiries into whether the price of gasoline has been illegally manipulated, said White House press secretary Scott McClellan.
President Bush is expected to announce the action this evening during a speech in Washington.
It's unclear what impact, if any, Mr Bush's investigation would have on prices that are near $3 a gallon. Asked if the president had any reason to suspect market manipulation, Mr McClellan responded: "Well, gas prices are high right now, and that's why you want to make sure there's not."
Republicans who control Congress have become concerned that the high cost of filling up could become a problem for them in the November elections. Polls suggest that voters favour Democrats over Republicans on the issue, and Mr Bush gets low marks for handling gasoline prices.
Republican House Speaker Dennis Hastert and Republican Senate Majority Leader Bill Frist urged Mr Bush in a letter Monday to order a federal investigation into any gasoline price gouging or market speculation.
McClellan said Mr Bush had already done so but had not revealed it publicly.
AP