Motorists have been getting some relief from high gas prices lately, with the national average price for a gallon of regular falling nearly 23 cents from this time last summer, according to the Energy Information Administration.

Oil analysts warn, however, that a major hurricane or refinery breakdown could send gas prices sharply higher. In addition, the recent bridge collapse in Minneapolis has prompted some lawmakers to propose raising the federal gas tax to pay for bridge repairs. (President Bush said he opposes the idea.)

One way to protect yourself against future oil shocks: Buy a fuel-efficient car. All the major automakers have rolled out high-mileage cars and trucks, and more are on the way. And if you buy a hybrid — a vehicle that combines an electric motor with a gasoline engine — you may be eligible for a tax credit when you file your 2007 tax return.

But if you're counting on the tax credit to reduce the cost of buying a hybrid, pay attention to the calendar.

The tax credit begins to phase out after an automaker sells 60,000 vehicles.

Once a manufacturer's sales hit the limit, buyers are eligible for the full credit until the end of the quarter in which the threshold was reached and through the next quarter. Then they're eligible for half the credit for six months. For the next six months, the credit will shrink to 25 percent of the full amount, then it will disappear.

If you're planning to purchase a Toyota Prius, the most popular hybrid, start looking. Toyota reached the 60,000 threshold last summer. Under the phase-out formula, taxpayers who buy a Prius before Oct. 1 will be eligible for a $787.50 tax credit. But after that date, you won't be able to claim a tax credit for the Prius, or any other Toyota or Lexus hybrid.

Currently, the maximum credit for Honda's 2007 Civic hybrid is $2,100. But Honda expects to hit the 60,000 mark in the third quarter, says spokesman Todd Mittleman. If that happens, purchasers of Honda hybrids will be eligible for the full credit through the rest of the year. In January, the credit will fall by half, dwindle to 25 percent of the full amount next July and evaporate at the end of 2008.

Other automakers have introduced new versions of hybrid vehicles in recent months. Tax credits for IRS-certified Ford Motor and General Motors hybrid vehicles range from $250 to $3,000. Nissan's Altima hybrid, which received IRS certification in January, is eligible for a $2,350 credit. Based on sales volumes so far, auto analysts don't expect these automakers to hit the 60,000 threshold soon.