Americans like to imagine the future. From the world's fairs of the early 20th century to futuristic magazine features in the 1950s to the 1980s "Back to the Future" films, we love dreaming up what might come next.

When we dream, it turns out, we dream without oil. The show-stealer at the Chicago World's Fair in 1893 was a demonstration of alternating current – a massive generator that made it possible to snuff out household oil lamps and switch on a light bulb. Doc's time machine in "Back to the Future" runs on garbage, and the "hoverboard" the hero in the film's sequels hops on to outrun the bad guys flitted on whimsy, not oil. And no one in the "Star Trek" franchise ever said, "Captain Picard, we need to swing by the gas station."

With today's volatility at the local pump, contentious debates about "peak oil," and soaring global interest in biofuels, imagining how the world looks without oil isn't just a fanciful distraction. There's lively debate about how far away a post-oil world is – earliest estimates are around 2030, while many analysts say that, as technology changes to accommodate fluctuations in the oil supply, we'll never technically see an end to oil. But advisory bodies such as the International Energy Agency and the US National Intelligence Council expect oil demand to spike, and supply to dwindle, over the next 15 years – which makes imagining a post-oil future an urgent task of the present.

There's no doubt that the world will look different – and not just a little bit different, suggests Dennis Bushnell, chief scientist at the NASA Langley Research Center in Virginia.

"After oil, we'll be in the virtual age," he says. Machines will take many more of our jobs. The ones we keep, we'll do by telecommuting. We'll still teleshop, but we'll probably buy less. "Physical universities will be a wasteland" by 2040, he predicts, as most degrees will be earned online. We'll even visit the doctor – and the Bahamas – virtually. "You [will] smell and feel the breeze, the sand, [and] the sun. You can do this at any time you want, anywhere you want, with anyone you want. Be anyone you want, and do anything you want," he says. "Machines are creating the world.... We're living virtually. This is the world 30 years out."

If these wild scenarios aren't far off, the circumstances they have in common – the absence of oil – is further out. Today's public is convinced it will never see an oil-free world. Less than one-quarter of Americans believe oil will run out in their lifetime, according to a September Christian Science Monitor/TIPP poll. Young adults are slightly more concerned: Thirty-eight percent of respondents ages 18 to 24 said it was "likely" they would see the end of oil.

Even oil industry experts acknowledge that having a stable supply of oil doesn't mean we must – or should – rely on it. A post-oil world may not be an inevitability to which we must react, but it may be a world we choose to create.

There are compelling reasons to make that choice, says Amy Myers Jaffe, coauthor of "Oil, Dollars, Debt, and Crises: The Global Curse of Black Gold" and director of the Baker Institute Energy Policy Initiative at Rice University in Houston. "They range from reducing our trade deficit to taking away instability in our financial system ... to global warming and protecting our environment."

It would be a mistake to see this element of free will as a hippie hangover or sneaky environmentalism. Whether we wait to run out of oil or choose to replace it before then may determine all that comes next. "How we leave the age of oil and what we set up for beyond that is really key to what the world looks like when there's a lot less oil," says Lisa Margonelli, director of the New America Foundation's Energy Policy Initiative. Do we update power grids to accommodate a surge in electric cars? Beef up public transit networks in less-urban areas? Bet on a biofuel breakthrough and plan for the adaptations that it would require? "There's a lot of differences among biofuels," says Ms. Margonelli. "An ethanol-based biofuel ... needs a whole different transit structure [than] a butane-based biofuel, or biodiesel, or biogas."

Choices made now about the coming energy transition will have a global effect. The Gulf states, home to "oil sheikhs," may see their influence fall. Some of those sheikhs, meanwhile, are moving away from oil: Saudi Arabia, an ally the United States has cultivated especially for oil, is making major investments in solar energy, both to use at home and sell abroad. Brazil, which along with the US is expected to produce most of the world's biofuel by 2015, may see its global clout rise.

And to Margonelli, at least, the Arab Spring suggests energy-rich regimes may suddenly see the wisdom of sharing the wealth domestically. "[Y]ou already see the beginnings of the next thing," she says. "The question is ... how do the dominoes hit each other as we go forward."

There are more concrete questions at hand as Americans imagine that way forward. Do we plug in our cars or feed them beets? Do we even still drive? Do we power our iPods by walking down the street, or cook dinner with stored solar energy? Not all of these scenarios are about oil substitution – none of us today toasts up a grilled cheese sandwich over a gasoline fire – but in the energy sector, the focus is broadly on alternative fuels, not just on oil replacements.

"The scenarios differ a lot depending on what the actual trigger is for the move away from fossil fuels," explains Patrick Tucker, spokesman for the World Future Society. "With mass depletion of oil, you get a price explosion, and this would have a really different effect than if we're able to move transitionally from oil as a result of application of sound technology."

That technology is exploding across the alternative energy sector. At the Massachusetts Institute of Technology, two architecture students sought to capture the energy released when people walk, jump, or run, hoping to recycle it for use in small electronic devices. The state of California is considering research on converting traffic vibrations into bankable electrical energy. Mr. Tucker expects a breakthrough within 20 years.

Other changes are closer at hand. Companies like NatureWorks in Minnesota and Telles in Massachusetts already use plant sugars to make everything from drinking bottles to diapers, pioneering biodegradable bases for otherwise petroleum-intensive plastics. Companies are discovering how to power cars with algae and air. Boeing jets using a mix of traditional fuel and biofuel have flown cargo across the Atlantic and passengers within Europe.

In those cases, the biggest change – what runs the engine – isn't necessarily visible. In other cases, the oil-conscious choice is much more noticeable. Take Google's "driverless" car, for example. Navigated by computers, which are much more efficient drivers than lead-footed humans, the cars have zipped quietly but successfully along California roads. This year, Google lobbied the Nevada Legislature to pass bills that would allow self-driving cars on public roads.

Letting computers or other robotic devices command the steering wheel could save a lot of energy. But, adds Tucker, "[You're] driving a car, and in a lane next to you is a robotically driven car? There would be some ... barriers to that."

The creepiness of rolling up next to a car without a driver suggests an even bigger change: an alternative highway system in the sky. "The same drone technology that the US military is using in Afghanistan could be put to use here to transport goods," Tucker says.

Whimsical as it may sound, Tucker's alternative highway gets at the other problem for oil substitutes and other alternatives: infrastructure. The kind of energy used isn't simply about what sources are available. It's about complicated systems built around energy already discovered.

"It's daunting to think about how you would start" an infrastructure change, says Ms. Jaffe. The incentive to face that challenge varies as oil prices fluctuate and alternative energies go in and out of vogue.

"In 2011, we're on track to spend a half a trillion dollars on gasoline alone at the pump," says Margonelli. "That's ... about $100 billion more than we spent on gasoline last year.... If you can come in with something that upsets the primacy of oil, there's huge market opportunity."

But alternatives markets can crash. Three US solar panel companies declared bankruptcy this year, due in large part to cheap Chinese competition and cuts to alternative energy subsidies in Europe. Even accepted alternative energies can face sudden setbacks. While much of Europe runs on nuclear power, this year's nuclear disaster in Japan prompted Germany and Switzerland to call off their nuclear programs, and Italy and Poland to reconsider plans to invest in the technology.

Overcoming inertia on alternative energy is about something else: the loony factor. "If you were the guy at Xerox 30 years ago who had this idea about e-mail or the Internet, you would've sounded crazy," Jaffe says.

Margonelli thinks progress toward a post-oil world will also be about something a bit more old-fashioned than vision or creativity. "Going after energy has this whole sort of patriotic, future-focused side to it: the feeling, which is in many ways a patriotic feeling, of needing to leave our children a world that's better off than what we found."