Oil prices are up to $145 a barrel. No, they're down to $55.

The roller-coaster ride may be making U.S. drivers happy - or at least saving them some of the extra money they spent going to work and on vacation this summer. But coupled with the credit drought, it's enough to give the alternative-energy industry vertigo.

Or worse. At least 10 U.S. ethanol producers reportedly have filed for bankruptcy in recent months, including VeraSun Energy Corp. of Sioux Falls, S.D., a billion-dollar business.

Even T. Boone Pickens is feeling a pinch. The billionaire oilman, who peppered the airwaves this summer and fall with commercials touting his proposals to promote wind power and natural gas to help wean the United States from imported oil, says his plans for a huge Texas wind farm may be slowed by reduced access to credit.

"He's certainly not alone. This is an economy-wide credit crunch," said Rob Gramlich, policy director of the American Wind Energy Association.

To environmentalists and others who follow the energy markets, the blow to alternative energy brings back worrisome memories of the 1970s and '80s.

Then, oil-price shocks linked to Mideast turmoil sparked a flurry of alternative-energy investment and development. But when demand softened because of conservation and the early-'80s U.S. recession, oil prices came back down and interest in energy issues faded.

Could that happen again? Energy experts say a repeat is unlikely, if only because worldwide demand is expected to drive up oil prices when the economy recovers, and because concerns about climate change are likely to persist.

But in the short run, those experts say the 18-month rise in oil prices and their sudden, steep fall are wreaking havoc - and offering opportunity.

Lower gasoline prices for consumers are a "silver lining in a dark economic storm," said John Hanger, Pennsylvania's acting secretary of environmental protection and former president of PennFuture, an environmental and energy advocacy group.

Hanger said a report this week by the International Energy Agency, which predicted strong long-term demand for oil and other fossil fuels, showed that the recent dip in oil prices from July's $147-a-barrel peak would be short-lived.

"The IEA data pretty much indicate that the $147 in July wasn't a product of market manipulation, it was a function of underlying supply and demand," Hanger said.

Hanger, who recently helped win passage of incentives for Pennsylvania's renewable-energy producers, said the recent drop offered a break from the financial pressures caused by this summer's record oil prices. But he said it should not distract anybody from what should be the nation's long-term goal for political, economic and environmental reasons: reducing U.S. dependence on fossil fuels, and especially on imported oil.

"It is one thing economically to buy 60 percent of your oil from overseas when it's $20 a barrel. It's quite another when it's $50 or $150 a barrel," Hanger said.

Still, Hanger said current oil prices could scare off investors in some energy alternatives, such as plants to turn coal into liquid transportation fuel. He said that according to some estimates, coal liquefaction may not be financially viable if oil stays below $80 a barrel.

Pennsylvania's fledgling biodiesel industry already has suffered - though more from volatility in prices for its feedstocks, such as soybean oil, than because of crude oil prices, said Ben Wootton, president of Keystone BioFuels of Shiremanstown, Pa., and founder of a group of biodiesel producers.

As recently as mid-2007, soy-oil futures traded at less than 18 cents a pound, Wootton said. This summer, they spiked above 75 cents - a price he said would push biodiesel's wholesale price above $6 a gallon.

Wootton said prices also spiked for other feedstocks, including beef tallow, chicken and pig fats, and even restaurant grease.

"Wall Street was in there speculating that people were going to be moving to alternative energy, and that was driving up our prices," Wootton said.

Thankfully for biodiesel producers, feedstock prices also followed oil prices down. On Wednesday, soy-oil futures for December delivery traded at 32.58 cents per pound at the Chicago Board of Trade, less than half their summer peak.

Even with the state's temporary incentives, this summer's commodity prices could have killed the industry, he said.

Some alternative-fuel producers have been wounded by attempts to outguess such a volatile market. That's what happened to VeraSun, which on June 30 reported six-month revenues up 388 percent from a year earlier, and a doubling of profits to $31.5 million.

At the time, when oil prices still were rising, corn was trading at about $8 a bushel, said Drake Lundell, editor of Ethanol & Biodiesel News, a trade publication. So to hedge against further increases, VeraSun locked in prices in the $6.75-to-$7 range.

By mid-August, corn was trading below $5 a bushel. Yesterday, it closed at $3.77.

"They would have looked like the smartest guys in the world if corn had gone up to $9 a bushel," Lundell said. On Oct. 31, VerSun sought protection from creditors in Chapter 11 bankruptcy.

Some energy experts say it's essential to take a long view.

Ralph Cavanagh of the Natural Resources Defense Council said this year's extreme volatility helps make the case for long-term investments in renewable energy and energy efficiency, especially when oil expenditures "go mostly to people who don't like us very much," Cavanagh said.

"For those who are not eager to repeat history, the lesson is to do everything possible to reduce demand and diversify supply away from fossil fuels."

Contact staff writer Jeff Gelles

at 215-854-2776 or jgelles@phillynews.com.