LOS ANGELES -- Good thing I was riding in a Ford Fusion hybrid gasoline-powered test car rated at 39 mpg city when I saw this Union 76 fuel price sign here this week: $2.10 per gallon for regular, $2.70 for premium, $3.70 for diesel. Three weeks earlier, driving a BMW 335d diesel around LA, I would have been moved to tears. At this station, diesel carries a 76% price premium over regular gasoline and a 37% premium over premium gasoline. Put another way: For $21, you could put in 10 gallons of regular unleaded, or 5.7 gallons of diesel. No way is diesel's greater efficiency (about 30%) going to make back that price differential. Nationwide, according to the Department of Energy, the average price of regular gasoline is $1.70 and the price of ultra-low-sulfur diesel is $2.53 per gallon.