WASHINGTON -- Sen. Arlen Specter is convinced that the consolidation of oil companies over the past decade is driving up gasoline prices and, after hearing from oil executives on Capitol Hill yesterday, he said he will continue working on legislation to create more scrutiny of mergers among the oil giants.

Troubled by rising gasoline prices coupled with soaring company profits, Mr. Specter, R-Pa., has prepared draft legislation that would prohibit the acquisition of an oil company if federal officials determine that the proposed deal may "appreciably lessen competition."

He noted his concern that there have been 2,600 mergers in the petroleum industry since the 1990s, and that the Government Accountability Office, or GAO, found in a 2004 report that the concentration has generally led to higher wholesale gasoline prices. ExxonMobil's 1999 merger was the largest, and just six years later, the company reported the largest corporate profit in U.S. history.

Mr. Specter's draft bill would direct the GAO to study whether the steps that the government has required oil companies to take as they moved forward with recent mergers adequately restored competition. And if the GAO determines that they did not, the bill would ask the Federal Trade Commission and the attorney general to consider unraveling some of those mergers.

The draft legislation also would address widespread suspicion among American consumers that oil and gas executives are stalling major projects -- such as tapping into vast natural gas reserves beneath Alaska's North Slope -- to keep profits high.

To that end, Mr. Specter's draft proposal would explicitly make it illegal for a company to refuse to sell existing supplies of gasoline or natural gas "with the primary intention of increasing prices or creating a shortage."

Several senators, including the Democrats' assistant minority leader, Richard J. Durbin of Illinois, have expressed interest in co-sponsoring the proposal.

Mr. Specter summoned a half-dozen of the nation's top oil executives before the Senate Judiciary Committee yesterday, along with academics, state attorneys general and some of the lawyers who have participated in major anti-trust lawsuits against the oil firms in recent years.

Oil executives told senators that it is the price of crude oil and increasing world demand, particularly among populous developing nations such as China and India, that has led to higher prices -- not the consolidation within their industry.

Their testimony was endorsed by Severin Borenstein, a business administration and public policy professor at the University of California-Berkeley's Haas School of Business, who said growing demand will continue to drive increases. "The main reason gas prices are so high is out of our control," he said. "The idea that Americans have a right to cheap, plentiful energy supplies is just out of sync of reality. ... As long as we are using oil as a transportation fuel, we are going to continue to be held up by the world oil market."

Nearly all of the executives told senators that mergers and acquisitions have made the industry more efficient and made it possible for their companies to undertake expensive exploration projects for new sources of oil and gas that can often end in failure.

"It takes an extraordinary level of financial strength to deploy such large amounts of capital in risky environments and a cyclical industry," John Hofmeister, president of Shell Oil Co., told the senators yesterday. "Fragmented or financially insecure players cannot afford such risk. To achieve what we have set out to do, we need your help -- not new barriers."

But several panel members who have challenged the oil firms said there was no question that consolidation has constricted supply, particularly of natural gas. The average price of natural gas rose 23 percent this winter over last winter.

David Boies, a lawyer representing a state agency in Alaska that has brought an anti-trust lawsuit against ExxonMobil and BP America Inc., detailed his client's allegations that the two oil firms are coordinating to stall production of some 35 trillion cubic feet of natural gas -- about 1 ¹/₂ times the amount the United States used last year -- on Alaska's North Slope.

The two companies control about 67 percent of the reserves, and ExxonMobil's CEO told senators that he has been working on the project since the mid-1980s. But the state agency alleges that the firms have refused to cut a deal on building a pipeline to bring the gas to market.