WASHINGTON, June 4 (Reuters) -

A group of Democratic U.S. House lawmakers asked the Justice

Department on Tuesday to probe allegations of antitrust behavior

among U.S. oil producers and OPEC and said the two largest U.S

oil companies have been conspiring to keep fuel prices high.

Nine House of Representatives Democrats, in a letter to

Attorney General Merrick Garland, cited a complaint by the

Federal Trade Commission (FTC) in May that alleged that the

former CEO of Pioneer Resources engaged in an "outrageous

scheme... to coordinate pricing between U.S. oil companies and

foreign producers."

The letter, led by Jerrold Nadler, the top Democrat on

the House Judiciary Committee, also cited the big profits earned

last year by Exxon Mobil Corp ( XOM ) and Chevron ( CVX ), the

two largest U.S. oil companies.

"Major oil producers appear to be colluding with each

other and foreign cartels to keep prices high, padding their

profits at the expense of American consumers," the lawmakers

said.

"We urge you to use the full authority of the Department

of Justice to investigate and, where necessary, prosecute this

anticompetitive conduct," the letter said.

On Exxon and Chevron ( CVX ), the lawmakers said: "But

apparently, instead of passing those profits through to

consumers in the form of cheaper products, the oil giants have

been lining their own pockets while conspiring to keep prices

high."

Exxon and Chevron ( CVX ) did not immediately respond to a

request for comment.

The Organization of the Petroleum Exporting Countries

also did not immediately respond to a request for comment.

In addition to Nadler, the letter was signed by Henry

Jackson, Pramila Jayapal and seven other Democrats.

Last month, the FTC approved Exxon Mobil's ( XOM ) $60

billion purchase of Pioneer Natural Resources, but barred former

Pioneer CEO Scott Sheffield from Exxon's board on allegations he

attempted to collude with OPEC to raise oil prices.

Late last month, U.S. Senate Majority Leader Chuck

Schumer and 22 of his Democratic colleagues

sent a similar letter

to Garland.

Sheffield coordinated efforts with U.S. shale oil

producers to constrain their output and raise energy prices, the

FTC said on May 2.

Sheffield, known for his long tenure and frank comments

on industry output and spending, used his influence "to align

oil production across the Permian Basin in West Texas and New

Mexico with OPEC+," a production group that includes Russia as

well as OPEC members, the FTC said at the time.

Sheffield's lawyers have referred to comments made last

month, when Sheffield asked the FTC to dismiss the ban. "At no

time did government officials and Mr. Sheffield exchange

competitively sensitive information," said Sheffield's counsel

Cleary Gottlieb Steen & Hamilton.