Washington DC - President Joe Biden has asked a US anti-trust regulator to investigate whether energy companies are ripping off consumers who are angry over sky-high petrol prices.

Biden sent a letter to Lina Khan, the head of the Federal Trade Commission, in which he calls attention to "mounting evidence of anti-consumer behavior by oil and gas companies."

The president compared the pain many Americans were feeling at the pump to the profits being reaped by US oil giants.

The letter noted that the "two largest oil and gas companies in the United States" – ExxonMobil and Chevron – are forecast to double their net profits compared to 2019, before the pandemic. In addition, they have announced plans for multibillion-dollar share buybacks and dividend payments.

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As evidence of potentially dubious behavior, the letter notes that prices for consumers at fuelling stations have remained high despite a decline in the price of unfinished gasoline for refiners.

"This unexplained large gap between the price of unfinished gasoline and the average price at the pump is well above the pre-pandemic average," the letter said.

"I do not accept hard-working Americans paying more for gas because of anti-competitive or otherwise potentially illegal conduct," the president wrote.

The FTC is an independent agency within the US government and not subordinate to the White House.

Ten months into his presidency, Biden's approval ratings are falling as inflation climbs. The appeal to the competition regulator is largely seen as a symbolic gesture to show sympathy for frustrated motorists.

ExxonMobil and Chevron's stock prices were largely unaffected by Biden's letter.