When the Toyota Prius debuted 11 years ago, it set the bar for ultralow fuel consumption on regular gasoline, but it did so with a highly complex and expensive hybrid powertrain. Today's compact Prius c, at just under $20,000 and 50 mpg combined, is a lot cheaper and more impressive. Along with its egg-shaped bigger brother, the Prius models are still the most fuel-efficient cars on sale in the U.S., diesels included.

But fuel efficiency, despite the government's insistence that automakers reach a 54.5-mpg fleet average by 2025, still isn't the prime reason we buy cars. Space, comfort, size, utility and fun all factor into our decisions. Thankfully, there's a fuel-saving feature on at least 77 new cars and trucks that not even the Prius has: direct injection. And it just happens to produce more horsepower, too.

With an engineering degree, you'll love knowing how these piezoelectric injectors make the stoichiometric gas-and-intake mixture denser and ignite the fuel closer to the spark plug, but I'll let ex-Car and Driver Editor-in-Chief Csaba Csere do that here and here. For the rest of you, including me, here's the short explanation: Instead of fuel being mixed with air above the intake, as with traditional fuel injection, the gas is sprayed at high pressure directly into each cylinder. The spray can be expertly fine-tuned by the engine's computer, allowing for faster, more complete combustion. The result is less fuel consumption, less pollution (General Motors says it reduces cold-start emissions by 25 percent) and greater power. If you see GDI, FSI, DFI, SIDI, Skyactiv or EcoBoost on a car's spec sheet or advertising, it's referring to direct injection.

Right now, the technology's premium -- estimated at one point to be hundreds of dollars extra -- is likely moot. Hyundai offers direct injection on seven of its models, including the Sonata and entry-level Accent. Kia does the same on five of its models, including its cheapest Rio. Chevrolet packs it on the V6 Camaro and on the current Impala -- very strange in a car that advertises a CD player as its coup de grace. Audi offers it on every model, including the V10 R8 and 12-cylinder A8. (Diesel engines have used direct injection for many years, but only the people who've bought VW TDIs truly know about that.)

Here's why direct injection matters. Before the 3.5-liter V6 in the Mercedes E350 received direct injection, it was delivering 268 horsepower and a rather lousy EPA rating of 17 mpg city/24 mpg highway. Now, thanks in good part to direct injection, the E350 pumps out 302 horsepower and achieves a respectable 20/30 rating. Mazda's transformation is even more remarkable. The 3 with Skyactiv direct injection and a 6-speed automatic transmission returns a whopping 40 mpg highway, while the 3 without direct injection (and one fewer gear) gets only 33 mpg. Both use the same 2.0-liter engine, although Mazda tacks on options and makes you pay $3,500 more for the Skyactiv model. The Porsche 911 has been on direct injection since 2009, and the yellow Carrera I just extolled achieves a remarkable EPA 20/27 rating, nearly matching the Benz sedan.

Ford's EcoBoost engines pair direct injection with turbocharging, so it's no longer strange that 4-cylinder Explorers or V6 F-150s with 420 lb-ft of torque can exist. All Buicks have it. So does every BMW save for three models. Even Bentley has gotten into the act, by adding direct injection to its new Continental V8 for (somewhat) better gas mileage.

However, direct injection isn't the only reason today's cars are getting substantially better mileage from one model year to the next. Advances in automatic transmissions, lighter vehicle weights, aerodynamic tweaks and auto start-stop systems all make an impact. But nothing else has made a more significant improvement within the engine itself.

Reliability has proven fine in the past few years, but a few automakers have experienced setbacks. Some Audi and Volkswagen engines with direct injection, as late as 2008, were known to leave heavy carbon deposits on the valves, which would degrade performance. The same problems were noted in Lexus models. In February, Nissan had to recall 250,000 cars with direct injection because of potential fuel leaks.

Toyota, Mitsubishi, Suzuki, Chrysler, Volvo and Subaru have yet to embrace the technology. Mitsubishi was a direct-injection pioneer in 1996 but doesn't offer it on any current U.S. models. Honda will offer direct injection for the first time on the 4-cylinder 2013 Accord.

Some automakers are also pursuing alternative injection strategies, such as Nissan's Dual Injector System, which places two conventional fuel injectors above each cylinder. Nissan says this system offers similar benefits at a 60 percent reduced cost. Lexus uses both regular and direct injection in some of its engines, which the company says improves midrange torque. Fiat and the upcoming Dodge Dart use MultiAir, a hydraulic system that micromanages engine valves to reduce fuel and increase power by an estimated 10 percent. An experimental technology called Homogeneous Charge Compression Ignition promises to make gasoline perform with diesellike efficiency by removing the spark plugs.

Keep all this in mind if you're shopping for a more expensive hybrid or electric car. Direct injection won't solve all of our fuel woes, but it proves one important thing: The internal combustion engine has a long life ahead of it.