"Now suddenly you're a big champion of coal?" Obama said.
The sparring on energy was one of the most heated exchanges in the debate with both candidates trying to attract economically minded voters along coal seams, in oil patches and in industrial towns.
When Obama emphasized his "all of the above" energy plan, it sparked a combative back-and-forth duel with a subtext about who would create more jobs by permitting the private sector to develop fossil fuels on public land and on the outer continental shelf.
Romney: "That's the problem. In the last four years, you cut permits and licenses on federal land and federal waters in half."
Obama: "Not true, Governor Romney."
Romney: "So how much did you cut it by --"
Obama: "Not true."
Romney: "By how much did you cut them by then?"
Obama: "Governor, we have actually produced more oil --"
Romney: "No, no, how much did you cut licenses and permits on federal land and federal waters?"
Obama: "Governor Romney, here's what we did: There were a whole bunch of oil companies --"
Romney: "No, I had a question, and the question was how much did you cut them by? How much did you cut them by?"
Obama: "You want me to answer a question? I'm happy to answer the question."
Both candidates bow to renewable energy
There were also sharp exchanges on renewable energy, with Romney making his boldest statements on that issue since the campaign began. The statements followed months of attacks on Romney by Obama for opposing the production tax credit, which benefits generators of wind energy in Iowa, Colorado and other swing states.
"I believe very much in our renewable capabilities -- ethanol, wind, solar -- would be an important part of our energy mix," Romney said. "But what we don't need is to have the president keeping us from taking advantage of oil, coal and gas."
The president, meanwhile, made a strong argument for more efficient use of gasoline through alternative vehicles and strengthened fuel economy standards. It was perhaps a peek into his energy priorities if he's re-elected; Obama has been vague about the policies he would pursue in his second term.
"But we've also got to continue to figure out how we have efficient energy, because ultimately, that's how we're going to reduce demand, and that's what's going to keep gas prices lower," he said.
But advocates are increasingly saying that Obama needs to provide the nation with a reason for converting its energy systems into ones that use cleaner power. Without describing the impacts of climate change, there's less motivation to undertake an expensive overhaul, they say.
"Both candidates vied to restate their commitment to more dirty oil, gas and coal production while ignoring the contradiction between an 'all of the above' energy program and reducing emissions of climate disrupting gases," Erich Pica, president of Friends of the Earth Action, said in a statement after the debate. "'All of the above' is not an acceptable energy policy or a responsible climate policy. It's a highway to hell -- a road to deeper droughts, fiercer fires and storms, messier spills and dirtier air."
Still, some Democratic strategists believe Obama has little to gain by addressing climate change three weeks before an election that might pivot on the electoral votes of hard-to-win states like Ohio, Virginia and Colorado.
"The lion's share of folks of who care about climate change know that he's a much better alternative than Romney, and he doesn't have to do a whole lot of education there," said Joe Trippi, who advised past presidential candidates. "The question is, how useful is highlighting the [climate] issue to pull some of these swing voters over with him?"