On your next trip to the car dealership, you might feel like you've wandered into a science lab. The old-fashioned cars that run on gasoline will be parked among a growing array of hybrids, a turbodiesel or two, and some newfangled contraptions with mileage well above 50 mpg. Chevy might tout its "extended-range" Volt; Nissan, its all-electric Leaf. An enthusiastic salesperson might even rhapsodize over fuel cell vehicles, just a few breakthroughs away. After decades of creeping improvements in efficiency, there's been an explosion of innovation. "We're going to see a faster ramp-up of fuel economy technology over the next three years than we've ever seen before," says Karl Brauer, senior analyst at car-shopping site Edmunds.com. "Improved mpg is here to stay."

Partly, that's due to sharp increases in government mileage requirements, which call for cars to average 35.5 miles per gallon by 2016. The oil price spike in 2008 also helped, by reigniting fears of scarce petroleum and wallet-emptying fill-ups. The Japanese, meanwhile, keep building better hybrids. And General Motors, Ford, and Chrysler are finally fighting back. Buyers who haven't traded in a car for a while may find that they can easily lower their tailpipe emissions and double their gas mileage, without settling for an underpowered wheezermobile. What may be most surprising is that some gas and diesel models are now nearly as thrifty as hybrids. Here's how the latest technologies are helping boost mileage: 

Hybrids. You now have a choice of nearly two dozen hybrids, including sedans, compacts, SUVs, luxury models, and even a sports car, the Honda CR-Z. Whereas the first hybrids offered great mileage but weak performance, most of the new models feature power comparable to gas-powered competitors, with mileage that's 30 or 40 percent better. The Ford Fusion hybrid, for instance, has been one of the most popular, thanks to ample power, a plush highway ride, and average mileage of 39 mpg. The Toyota Prius handily beats it on mileage, averaging 50 mpg, but with wan acceleration.

Hybrids still cost more, so buyers interested in saving more than the environment can roughly calculate their break-even point using the price of competing models, the mpg difference, and annual miles driven. Edmunds.com estimates that the break-even period for the Toyota Camry hybrid for the average driver (logging 15,000 miles per year) is a mere 1.3 years; after that, the owner would save money by buying less gas. But for the Lexus LS 600h L, the break-even point is an absurd 108 years, mainly because the car costs $30,000 more than a comparable gas-powered model, with only a modest mileage improvement. Tax credits in some states can reduce the break-even period, but many subsidies and perks once offered for hybrids have expired or been transferred to newer-tech vehicles.

Turbodiesels. Diesels, which nearly disappeared from U.S. roads when several states hiked emissions standards to levels that the smoky old models of yore couldn't meet, are making a comeback, thanks to low-sulfur fuel and new "clean diesel" technology. They're appealing because the fuel contains more energy than gasoline, so it provides better performance and efficiency both. The Volkswagen Golf TDI, for example, averages 34 mpg while outmuscling most other compacts. That's typical. 

The fuel costs about 20 cents more per gallon than regular gas, and the cars are a bit pricier, too. But they also have fewer parts and tend to last longer. Edmunds reports that the break-even period for diesels is often shorter than for hybrids. The BMW 335d sedan, for instance, earns back the extra cost through higher mileage after about four years, and the "BlueTEC" version of the Mercedes M Class SUV does after just one year. 

Electrics. The federal government has sweetened the deal with a $7,500 rebate on electrics, which brings the price of the Nissan Leaf down to about $26,000 and the Chevy Volt down to about $34,000. (The forthcoming 2012 Prius plug-in hasn't been priced yet.) If they catch on, these electric-powered cars could help transform the country's energy use. But for the time being, practical limitations make them unfit for most Americans. 

The Leaf, like the more exotic Tesla Roadster and Fisker Karma, runs completely on battery power. On the road it feels like an ordinary car, with decent pickup and seating for five. The catch is that it only goes about 100 miles on a charge; after that, you need to find an outlet and cool your jets awhile. Recharging takes about eight hours using a 220-volt outlet, the kind used for washers and dryers. The Leaf can also be "trickle charged" from an ordinary 110-volt outlet, but it takes a lot longer. The Volt can go about 40 miles on battery power before a small gas engine kicks in. The 2012 Prius plug-in will go perhaps 15 miles entirely on battery power, then operate like an ordinary hybrid.

The gas required for a typical conventional car adds up to about 13 cents per mile, if gas is at $3 a gallon. Electrics cost about 3 cents per mile, and less if they're charged overnight, when rates are generally lower. And while fossil fuels are usually required to generate the electricity that recharges the battery, there are no emissions from a car operating on electric power. If guinea pigs--er, early adopters--are wildly enthused, more buyers will line up, and the technology will get better and cheaper. But for most buyers today, an electric car is not a practical option.

Gasoline. The internal-combustion engine is getting a lot more efficient too, thanks to better transmissions, fuel-sipping injectors, and other technology. The new Ford Explorer, for instance, is shedding its burly image with four- and six-cylinder engines--but no V-8. Yet it can still carry up to seven people and tow a boat. The Explorer's top highway mileage rating will be in the high 20s, compared to just 21 mpg for the outgoing model. Other new or forthcoming models like the Mazda 2, Ford Fiesta, Chevy Cruze, Hyundai Sonata, and Fiat 500 get mileage ranging from the high 20s to high 30s--better than some hybrids. Even muscle cars like the Ford Mustang and Chevy Camaro now average mileage in the mid to high 20s.

Other alternatives. Honda's natural-gas-powered Civic GX averages the equivalent of 28 mpg, and since natural gas is cheaper than gasoline, fueling costs are about 25 percent lower. Natural gas also burns more cleanly. But there are fewer than 1,000 natural gas refueling stations in the whole country. Ethanol usually isn't worth the bother, since it costs more per mile than gas. Hydrogen-powered fuel cell vehicles like Honda's FCX Clarity prototype may have a future, if the technology matures and a network of fueling stations materializes. Hydrogen is the holy grail of fuels, since it's renewable, produces little pollution, and ought to be cheap, though the under-hood technology is still far from affordable. If you buy a gasoline-powered car in the next year or two, it could be your last. Or not.