Will you buy that SUV if gas hits $4?

Here's a question to ponder, especially if you're thinking about buying a new car next year.

If the price of gasoline hits $4 a gallon or more, do you really want to buy that big sport-utility vehicle?

One can easily bet that the top brass at Ford Motor (F), General Motors (GM), Chrysler, Toyota Motor (TM), Honda Motor (HMC) and Nissan (NSANY) are all thinking about how you'll answer the question, too. That's a big reason they're working on building and selling electric cars.

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Right now, the average price of gasoline is a touch above $3 a gallon, a level not seen since October 2008. Gasoline is up 15.3%, according to AAA's Daily Fuel Gauge Report, and 88% from the end of 2008.

Crude oil topped $90 a barrel last week and ended Monday at $91. That's up 14.7% for the year and 104% from the end of 2008.

The consensus is that crude oil will continue to rise in 2011, probably above $100 a barrel, with pump prices rising to $3.80 to $3.90. Maybe even $4.

Analyst Peter Beutel sees prices rising 50 cents to 70 cents a gallon by May.

"There is nothing to stop prices from advancing, and we may see them rise until they wreck the recovery," he wrote in an e-mail. 

John Hofmeister, the former president of Shell Oil, suggested on Platt's Energy Week television that the retail price of gasoline will hit $5 a gallon by 2012. Others think that may be early.

What's not clear is whether a 34% increase in gasoline next year will change spending habits.

Since incomes aren't showing similar gains, the answer is probably yes.

So far, the jumps for crude oil and gasoline have not hurt the automaker stocks. Ford shares are up 37% since the end of September. Toyota, Honda and Nissan are up between 5% and 10%. GM is up about 5%. But the group has been largely flat for the past few weeks.

But wait. The vulnerabilities are there because much of the improved performances of all the automakers came from big vehicles.

Sales of Ford's F-series pickups were up 26% through November. Chevy Silverado sales are up 16%. And Toyota Tundra sales are up 17%.

It's like the good old days -- before 2007 and 2008, when fuel prices shot up -- are back again.

There is, of course, a difference. This year, the economy is growing, albeit modesty. In 2007 and 2008, the economy was falling apart.

How much of consumers' budgets are taken up by gas prices varies. In states including Montana, Louisiana and Mississippi, Texas, Oklahoma and Arkansas, 10% of disposable income goes to filling gas tanks, according to a new study by PortiaGroup. It's less than 6% in New York, Illinois and Massachusetts.

Montanans spend more than 12% of household income on fuel. New Yorkers spend just 4.7%.

PortiaGroup's study uses data from the Oil Price Information Service, the company that collects the data for AAA's Fuel Gauge report.

The common explanation for rising gas prices is growing global demand. Add to that the huge dollars pouring into futures trading for gasoline. The speculation cuts two ways: Some traders are simply betting on great demand. Others are using oil to hedge against expected inflation.

There are winners from the oil run-up: oil stocks. The NYSE Arca Oil Index ($XOI.X) is up 8.7% this month and 15% for the quarter. The Philadelphia Oil Service Sector Index ($OSX) is up 6.4% for the month and 21.5% for the quarter.

Refiner and retailer Valero (VLO) is up 18% this month and 31% for the fourth quarter. Exxon Mobil (XOM) has risen 5% this month and 18.2% for the quarter. Chevron (CVX) is up 11.3% in December and 11.2% for the quarter.