“Even if it is legal, if every member of Congress pushed for industries that they have financial ties to, there would be an outcry from the public,” said Robert M. Stern, a California lawyer who has helped draft state ethics and campaign finance laws.

Mr. Boren often works in close coordination with the lobbying and promotional groups in Washington financed by the natural gas industry in an attempt to wield influence in a city where energy debates have long been dominated by oil and coal interests.

Mr. Boren, 38, a conservative four-term Democrat, has announced that he will not seek re-election next year. Instead, he plans to return home and work in the private sector — he would not say with what industry — and consider a run for governor. Whatever happens, he said, he will continue to promote Oklahoma’s natural gas industry.

“It is a part of who we are,” he said. “East Coast liberals don’t really have a frame of reference. They are eager to get the resource — and heat their homes — but they don’t understand us.”

One of Dan Boren’s first jobs out of college was in oil — as vice president of the small company run by his stepfather, John C. Robbins, in East Texas. Energy industry executives helped drive his political career, urging him to follow the lead of his father and grandfather, Lyle Boren, and run for Congress in 2004 after one term in the Oklahoma House.

“It’s in your blood,” Mike Terry, president of the Oklahoma Independent Petroleum Association, recalls telling Mr. Boren. “It’s part of your heritage. And we need you there.”

The pitch came just as a revolution in natural gas drilling was ignited.

Devon Energy, a business based in Oklahoma that is now one of the nation’s largest natural gas companies, had bought out a competitor whose owner had perfected the fracking technique, which uses a mixture of water, sand and a soup of chemical lubricants to free natural gas trapped deep underground in the pores of dense shale rock.