Oil futures edged higher Tuesday as a falling dollar and rising supply concerns again brought buyers into the market. Retail gas prices, meanwhile, slid below a national average of $4.07 a gallon.

Oil followed a months-long pattern: When the dollar loses ground, investors tend to buy crude and other commodities seen as a hedge against inflation. Also, a weaker dollar makes oil less expensive to investors dealing in other currencies. Many analysts believe the dollar's protracted decline has been one of the main reasons oil has nearly doubled in value over the past year.

But Tuesday's gains were limited by concerns about the impact high prices are having on demand, and worries about Congress' increasing scrutiny of the oil market.

Light, sweet crude for August delivery rose 11 cents to $136.85 a barrel on the New York Mercantile Exchange after fluctuating in earlier trading.

Prices were also supported by recent production outages in Nigeria. But reports of an oil workers strike, which helped push prices higher on Monday, were denied by Babatunde Ogun, president of Pengassan, Nigeria's white-collar oil union.

"There's no strike," Ogun said. "We're trying to settle the matter."

Ogun said talks continued Tuesday among his union, Chevron Corp. and government mediators in Nigeria, Africa's largest oil producer and a major U.S. supplier.

OPEC President Chakib Khelil insisted Tuesday that oil producers saw no need to raise supply, blaming high prices on factors such as U.S. pressure on Iran over its nuclear program and the weak dollar. Khelil's comments came days after Saudi Arabia disappointed the crude futures market by saying it would boost production less than many had hoped.

Also lifting prices were new sanctions against Iran approved by European Union nations on Monday, imposing additional financial and travel restrictions on a list of Iranian companies and experts including the country's largest bank. The 27-nation bloc stopped short of banning oil and gas exports from Iran, OPEC's second-largest producer, in response to its nuclear program plans.

A litany of recent reports from the Energy and Transportation departments has offered concrete evidence American consumers are driving less in response to high prices. At the pump, the average price of a gallon of regular gas slipped 0.3 cent overnight to $4.069 a gallon, according to a survey of stations by AAA, the Oil Price Information Service and Wright Express. Still, prices are $1.09 higher than a year ago.

"We're seeing demand deterioration in the U.S.," said Jim Ritterbusch, president of energy consultancy Ritterbusch and Associates in Galena, Ill.

Vienna-based JBC Energy predicted U.S. gasoline demand will fall 1.7% this year compared to 2007, citing Department of Transportation reports showing that U.S. vehicular traffic fell by 2.1% between January and April of this year compared to the same period last year.

Increased scrutiny of oil trading practices is keeping some potential investors on the sidelines, analysts said. Democratic members of Congress said Monday they intend to tighten restrictions on pension funds, investment banks and other large investors that they blame for driving up fuel prices. Additional hearings were being held Tuesday.

In other Nymex trading Tuesday, July gasoline futures rose 2.23 cents to $3.4774 a gallon, and July heating oil futures rose 3.9 cents to $3.8354 a gallon. July natural gas futures fell 13 cents to $13.073 per 1,000 cubic feet.

In London, August Brent crude futures rose 77 cents to $136.68 a barrel on the ICE Futures exchange.