There's one rule that all car owners learn, usually the hard way: Cheap gas doesn't stay cheap.
So if you're counting on your next car to save you money on gas, there are some shopping strategies and new technologies that can help you reach that goal. Here are three tips to keep in mind.
Tip 1: Consider gpm, not mpg
Consumers are used to the miles per gallon yardstick for measuring a vehicle's fuel economy. But it's not the only way to think of fuel efficiency. Considering gallons per mile rather than miles per gallon gives a much more precise idea of how much gas and money a new car will save you, says Richard Larrick, a professor at the Fuqua School of Business at Duke University.
Here's how it works: First, pick a certain number of miles you drive in a given period of time. Larrick uses 10,000 miles per year, because it's round and close to most Americans' annual mileage.
Divide that number by a vehicle's mpg and you get the number of gallons of gas a vehicle burns over that distance. For example, take an SUV that gets 12 mpg. A car owner who drives 10,000 miles per year would consume 833 gallons of gas. In other words, it has a gpm of 833 gallons per 10,000 miles.
An upgrade to a more fuel-efficient SUV -- one that gets, say, 14 mpg -- doesn't sound like much of an improvement. But by the gpm yardstick, the new SUV clocks in at 714 gallons per 10,000 miles -- a savings of 119 gallons of gasoline. At last week's average price for regular unleaded in Seattle, that's a savings of $341.
At the low end of the mpg spectrum, in particular, very small improvements yield big savings, Larrick says.
"I really want to get people out of the 15 mpg cars," he says. "Ideally, they end up at the 60 mpg car, but the important thing is the recognition that we should get them from the 15 mpg car to the 30 mpg car."
Tip 2: Get turbocharged
High-end hybrids and electric cars are garnering the most publicity these days. But automakers are also putting other technologies to work to improve the fuel economy of conventional vehicles.
One example is the turbocharged engine, which recycles super-hot exhaust back into the engine to improve the engine's energy efficiency and power.
Until recently, turbocharged engines have largely been confined to European markets and high-end sports cars, but that is starting to change. Ford, for example, has brought turbochargers to the mainstream car market with its EcoBoost engine.
Ford plans to introduce the direct-injection turbocharged engine in 90 percent of its models by 2013. The automaker says it improves fuel economy by up 20 percent and cuts carbon dioxide emissions by 15 percent without sacrificing power.
Tip 3: Think about diesel
A slew of European automakers are rolling out diesel-fuel models in the U.S. with fuel efficiency approaching that of hybrids. And now that diesel fuel prices in the U.S. have been falling closer to the price of gasoline, diesel vehicles may be a better value.
On average, drivers get 20 to 40 percent better mileage with diesel fuel, along with 50 percent more power. For example, Volkswagen's diesel-powered Jetta TDI gets 40 mpg in highway driving, according to the EPA.
Mercedes-Benz sells several "clean diesel" vehicles under its BlueTEC badge. Audi and BMW also offer diesel vehicles in the U.S.