Americans for Prosperity, a limited-government advocacy group, is airing a radio ad praising U.S. Sen. Elizabeth Dole's record on energy.

What it says: The ad begins with sounds of traffic. Two narrators, male and female, discuss high gas prices: "You've seen the bad news. We're pushing $4 a gallon and these skyrocketing prices are hammering North Carolina families. It's time for bold action, yet Congress hasn't lifted a finger." Light guitar music then plays. "But North Carolina is lucky. We have a senator who's leading the fight to lower energy prices, Elizabeth Dole. Senator Dole has a real plan to lower gas prices. It's called the Gas Price Reduction Act. The United States is home to a vast supply of oil, estimated at over 2 trillion barrels. The Dole plan lifts the ban on offshore exploration and oil shale development and continues to promote conservation. Senator Dole understands increasing production here at home means jobs for hard-working North Carolinians. Senator Dole has shown real leadership on the energy issue at a time when North Carolina families need it most. Call Senator Elizabeth Dole today at 919-856-4630 and tell her thanks for all she's doing to lower gas prices. Paid for by Americans for Prosperity, which is responsible for the content of this advertising and not authorized by any candidate or candidate's committee. On the Web at AmericansforProsperity.com."

The background: In late June, a group of Republican senators introduced a bill called the Gas Price Reduction Act.

The legislation, which mirrors several aspects of Republican presidential candidate John McCain's energy plan, would lift a Congressional ban on offshore drilling, promote oil shale drilling in three Western states, strengthen regulation of oil futures trading and make loans and grants to battery makers.

In a statement announcing her cosponsorship of the bill, Dole stressed that it would leave the decision on offshore drilling up to the state.

In a 2005 report, the RAND Corporation, a nonprofit think tank, estimated that a giant untapped oil shale deposit in Colorado, Utah and Wyoming could hold between 1.5 and 1.8 trillion barrels of oil, of which roughly 800 billion barrels could be recovered.

Neither offshore drilling or oil shale would increase the oil supply for a number of years, although supporters say that by expanding the potential supply they could affect current market prices, which are based in part on future supply.

The Energy Information Administration said in a report last year that offshore drilling would not increase the oil supply until 2017, while the RAND report projected that technical problems would prevent oil shale from producing a significant amount of oil for at least 20 years.

Offshore drilling in North Carolina could lead to jobs on oil rigs, building and maintaining pipelines and shipping, although it's not clear yet whether the oil would be processed here or elsewhere. Oil shale drilling would not directly lead to new jobs in this state.

The bill includes hundreds of millions of dollars in loans and grants to promote the development of new batteries for hybrid and plug-in vehicles.

It also directs a percentage of the federal revenue be used for land and water conservation and mitigation of affected wildlife areas.

Is it accurate? The ad is generally accurate, but it makes two claims that are misleading. The United States may have as much as 2 trillion barrels of oil, but not all of it is usable. The bill could lead to better hybrid cars, but it does not exactly promote energy conservation. Most listeners would not think the ad was referring to land and water conservation.

Does the United States have 2 trillion barrels of oil?

A radio ad touting an energy bill cosponsored by U.S. Sen. Elizabeth Dole says that the United States is "home to a vast supply of oil, estimated at over 2 trillion barrels."

The ad appears to be referring to the Green River Formation, a giant untapped oil shale deposit in Colorado, Utah and Wyoming.

A 2005 report by the RAND Corporation, a nonprofit think tank based in California, estimated that the Green River Formation holds between 1.5 and 1.8 trillion barrels of oil, of which roughly 800 billion barrels are recoverable.

"Present U.S. demand for petroleum products is about 20 million barrels per day, so 800 billion barrels would last for more than 400 years if oil shale could be used to meet a quarter of that demand," the think tank noted in a brief.

However, it added that there are technical problems.

"Assuming the private sector decides to invest in oil shale development and production, we expect that an oil shale industry capable of producing more than a million barrels per day is at least 20 years off," it said.