Despite remarkable advances in mainstream gasoline engines, the combustion cycle developed by Rudolf Diesel at the end of the 19th century continues to be more fuel-efficient. For one, diesel engines squeeze the air in their cylinders to such pressures that the injected fuel ignites with no need for an electric spark. And gallon-for-gallon, diesel fuel contains some 12 percent more energy than gasoline. The upshot: diesels consume about 15 to 30 percent less fuel over all.

Owners of heavy-duty pickups have long relied on these durable, hard-working engines, which have the reputation for running 300,000 miles and more. This fall, the 2014 Ram — among the mileage leaders on the gasoline side — will become the only light-duty pickup to offer a diesel, a 3-liter V-6 shared with Jeep. That innovation, in a pickup class that accounts for more than a million sales each year, is sure to be closely watched by Ford and Chevy.

About 6.7 million diesel vehicles were on American roads in 2012, according to R. L. Polk registration data, but barely 800,000 of those were passenger cars and S.U.V.’s; heavy-duty pickups and vans account for most of the remainder. That compares with 2.3 million registered hybrid models.

The number of available diesel car and S.U.V. models is expected to double by the end of 2014, to 34 from 17, according to the Diesel Technology Forum.

An industry analysis firm, LMC Automotive, projects that diesel market share will double by 2018, from 3.7 percent to 7.5 percent. That would rival the 8.7 percent for all hybrids and plug-ins combined. And battery-only E.V.’s? They’re expected to capture just 0.6 percent of sales.

The Germans are going all out. New Bluetec versions of the GLK-Class crossover and C-Class sedan will give Mercedes-Benz eight diesel models in its 2014 American lineup, including the E250 Bluetec, a 4-cylinder version of the E-Class sedan.

BMW will drop a 4-cylinder turbodiesel capable of 45 m.p.g. highway in its 2014 328d sedan and xDrive Sports Wagon in August, joining the X5 xDrive 35d S.U.V. and 535d midsize sedan in showrooms. Porsche, too, offers a diesel, in the Cayenne S.U.V.