Aug. 5, 2008 -- The rising price of gasoline has fueled an increasingly sharp debate between presidential rivals Barack Obama and John McCain, complicated by the fact that both men have shifted their positions on energy issues.
The most dramatic change for both candidates has been a growing willingness to accept offshore drilling for oil.
In recent months, McCain, R-Ariz., went from opposing offshore drilling to becoming an ardent supporter of it.
Obama, D-Ill., says he is still opposed to coastal drilling, but on Monday allowed that he would consider it as part of a comprehensive energy plan.
The presumptive Democratic nominee also suggested Monday that the government tap its strategic oil reserve to help bring down the price of gas, another move he once opposed.
Oil's Slippery Place on the Trail
The slippery issue of oil and energy supply has taken on greater prominence as voters fume over the price of gas and a growing number of Americans now approve of offshore drilling.
"I think that they're just competing with each other to do the most popular thing on the subject that voters care about most," said ABC News' Cokie Roberts on "Good Morning America."
And they've been trying to blame each other for the rising price of gas.
"John McCain. He's been in Washington for 26 years," intones an Obama ad that has been running in battleground states. "And as gas prices soared and dependence on oil exploded, McCain was voting against alternative energy, against higher mileage standards."
An earlier ad claimed that McCain was "in the pocket of big oil."
McCain, in turn, has tried to pin the country's energy woes on Obama, heaping much of the blame for the pain at the pump on the Democratic senator's opposition to coastal oil drilling.
Presidential Campaign Conversions
McCain is a fairly recent convert to offshore drilling.
It wasn't on his agenda nine months ago when he said, "I don't support drilling offshore in Florida or California."
Fast-forward to last Friday in Orlando, when McCain declared, "We need to drill more, drill now, and pay less at the pump."
Drilling now, the presumptive Republican nominee claims, will produce quick results.
"I met with the independent oil company executives recently who told me that they could utilize existing facilities to increase our oil supply in a matter of months and build new facilities in a very short space of time," McCain said in Panama City, Fla., on Aug. 1.
Experts think McCain's timetable is extremely optimistic.
Jim Burkhart of the Cambridge Energy Research Associates told "Good Morning America" on Tuesday that it would be more like a "five- to 10-year time frame... to have significant new supplies in U.S. waters."
Burkhart also chuckled at the McCain ad that asks, "Who can you thank for rising prices at the pump? Obama."
"It's not any one person. It's not any one country," Burkhart told "GMA." "We've seen prices rise for oil over the last few years because of a five-year period of unprecedented global prosperity."
Obama says he still opposes offshore drilling, but now says he might be willing to allow it.
"I am willing to consider it if it's necessary to actually pass a comprehensive plan," he said Monday, in a statement that surprised many of his supporters.
Fact-Checking the Candidates
Like McCain, Obama has made some statements that don't stand up to an expert fact-check, like his declaration last week that keeping your car tires properly inflated "could save all the oil that they're talking about getting off drilling."
Anne Mathias, director of Policy Research at the Stanford Group, found that comment overstated.
"Unless everybody in the country is driving a 1969 Chevy Impala or something like that with the tires at half inflation, you're not going to realize as much savings as he's talking about," she said.
But Frank Verrastro, Director and Senior Fellow at the Center for Strategic and International Studies (CSIS), told ABC News that if every American tuned their car and inflated their tires properly, the energy savings could amount to 800,000 barrels of oil a day.
McCain has said he supports the idea, but his campaign nonetheless mocked it, handing out tire guages to reporters and supporters.