U.S. automakers, late to recognize the sales implications of spiraling gas prices, have started to adjust their business models, in at least one modest respect: some luxury cars are now being designed to run on regular unleaded gasoline, USA Today reported Thursday.

Regular unleaded gasoline, with an 87 octane, typically costs 20-40 cents less than premium gasoline, with a 91 octane.

Ford (NYSE: F) and General Motors (NYSE: GM) are encouraging dealers to promote their no-premium-gas luxury cars' potential, as a selling point for consumers with budgets pinched by $4 per gallon gasoline, USA Today reported Thursday. Ford rose 5 cents to $4.99, while GM fell 15 cents to $10.10 in mid-day Thursday trading.

Auto mechanic Eddie Renn, based in Larchmont, N.Y., said the fact that automakers are manufacturing more cars designed to run on regular gasoline "is an improvement," but he questions why the automakers are using a lower gasoline cost as a selling point for luxury cars. Renn added that his auto repair business is not affiliated with any auto manufacturer.

Does gas price matter for luxury car owners?

"If you're driving a luxury car and you're concerned about a 20 or 30 cent difference a gallon, maybe you shouldn't be driving a luxury car." Renn said. "The luxury car owners who come in here [to his gas station] aren't concerned about the price of gas, I can tell you that."

Renn said most new cars, excluding sports cars and other vehicles, are designed to run on regular gasoline. A higher percentage of older cars -- particularly those built before 2000, require a higher octane, either mid-grade gasoline (also called 'plus') with an 89 octane, or the aforementioned premium gasoline, with a 91 octane.