LOS ANGELES — Panic buying and $4-a-gallon gas have increased the sale prices of hybrid cars and trucks in recent months to the point where, in some cases, the amount of time needed for a hybrid system to pay for itself has swelled by decades.

In March, when the per-gallon price of regular gasoline nationwide was 37 cents cheaper than it is today, there were four hybrid models — 30 percent of the market segment at the time — whose fuel savings could amortize the so-called hybrid premium in under 5 years based on 15,000 miles of travel annually.

The premium is the extra cost of a hybrid over that of the comparable non-hybrid model in the same manufacturer's lineup.

This month, with two new hybrid models in the mix, for a total of 15, there are only three models — 20 percent of the segment — with a reasonable chance of paying back the premium in less than five years: Toyota's Prius, Nissan's Altima and Chevrolet's two-mode Tahoe SUV.

The difference between then and now is the rise in gas prices and the rush to buy more fuel-efficient vehicles, which has stiffened sales prices for hybrids and increased the discounts dealers and automakers are offering on less-efficient conventional gasoline models.

These developments make it harder for the hybrid to earn back its price premium from fuel savings alone, although there are a few exceptions.

Ford's Escape hybrid SUV and its Mercury Mariner sibling and Saturn's Vue Green Line mild hybrid SUV all saw slight dips in the payoff period since March, while payback for Toyota's Prius remained unchanged, according to June figures prepared by Edmunds.com analysts.

The payback period for every other hybrid model went up. At the bottom of the pack was the Lexus 600h, which costs $18,858 more than the LS 460L, the most comparable non-hybrid model in the Lexus lineup. The 600h saves only $189 a year in gas versus the 460L.

If fuel prices and all else remained stable, it would take 99.6 years — 1.49 million miles of driving — for the big hybrid to earn back its price differential. That's up from 68.6 years, or a million miles, in March.

Chevrolet's mild hybrid Malibu didn't fare well either, the payback period rising to a hefty 11.1 years from just 2.7 years just three months ago. The Malibu Hybrid cost $1,867 more this month than the Malibu LT sedan (2.4-liter engine, four-speed automatic transmission) and would save only $169 a year in fuel costs.

What this means to you: If your primary goal in buying a hybrid is to save money, as opposed to making an environmental statement about yourself, be sure to do the math. — Scott Doggett, Correspondent