For many, the question isn't "will cars be powered differently in 40 years?" but whichnfuel will dominate — electricity (plug-in, or batteries or both?), biofuels (food-based ethanol, or something more advanced?), or hydrogen? (Really?)

But in a session at the MIT Energy Conference Saturday afternoon, analyst John Casesa, a one-time GM employee who spent 17 years on Wall Street before opening his own consultancy, says he doesn't envision much change:

"I don't see a dominant solution even 50 years out. Internal combustion is pretty compelling. Others will have only 10-12 percent each," he said.

John Viera, who works on sustainable business strategies for Ford, said he expects "movement away from petroleum," but a continued focus on liquid fuels, "probably cellulosic ethanol."

He added that he expects a portfolio of energy sources to develop worldwide, in part due to regional influences. "We think natural gas has a niche, in areas of China and in Thailand" for example, where supply is relatively accessible.

He said he expects natural gas to have a place regionally in the US, too, though he pointed out that there are 164,000 filling stations, 1,800 ethanol providers, and just 800 for natural gas.

Meanwhile, Viera said that Ford has "recently made a conscious decision to emphasize electricity in [its] advanced R&D." He said economic conditions have forced the company both to narrow its research objectives and to partner with universities and other institutions. "We're doing more partnering. One of the largest VCs around right now is the federal government."

Casesa said he foresees a long-term trend toward cleaner vehicles, and expects "start-ups to have an enormously disruptive effect." But in the shorter term, he said he expects the economy to mask that disruption.

"The auto industry is imploding. It's very capital-intensive, which makes it very vote-intensive, so I think we'll see some economic nationalism" as nations try to protect their automakers, as the US is doing in its funding for Detroit.