HOUSTON — Amid talk of cars powered by everything from ethanol to electricity to hydrogen, one oil company is betting big on another alternative fuel: diesel.

Marathon Oil Corp. is beginning construction of a $3.2 billion addition to its largest refinery, in Garyville, La. The current facility, like most U.S. refineries, makes about twice as much gasoline as diesel. The addition, which Marathon expects to begin production in the fourth quarter of 2009, will crank out roughly equal amounts of both.