The light-weight hybrid — especially Toyota's Prius and Honda's Civic — remains the popular choice of environmentally-aware car buyers, pushing annual hybrid sales to 345,000 (up 35 percent over 2006) and often leaving customers waiting for months for their green machine.

As pump prices continue to climb there's a new entry vying for attention on the eco roadway. It's the familiar diesel that's been newly refined to reduce unwanted emissions while retaining its ability to squeeze the most energy out of every gallon in the tank.

A spot check of Twin Cities Toyota and Honda dealers revealed that new hybrids are available where you once had to wait for months. But things are different at Volkswagen, with its popular Jetta TDI (for turbo diesel).

"I don't have a diesel available, but I'd be happy to put you on my list," said John Sabastian at Schmeltz VW in St. Paul.

Recent events have brought new interest in the diesel:

First, the U.S. Environmental Protection Agency's (EPA) changed its fuel-efficiency rating to better reflect actual driving, and the hybrid took a big hit. Rather than achieving upwards of 60 miles per gallon (mpg) as previously and widely reported, EPA's new ratings reflect what hybrid drivers were getting — from 40 to 44 mpg highway, but better in the city.

The hybrid is a gasoline engine and electric motor that are synced to shut off and turn on depending on energy requirements. Because the system relies on its electric motors in slower city driving while capturing energy from slowing and braking in stop-go traffic, its in-city mpg is better than on the road.

More power from diesels
Unlike the complicated and relatively new hybrid technology, the diesel engine is time-tested and simple. Its cylinders compress and superheat air so that fuel explodes as it's injected. No sparkplugs are needed to ignite the fuel, which means no complicated electrical systems. Diesel fuel contains more energy per gallon than gas, so its in-city mileage tops 40 mpg with drivers often getting 45 mpg on the highway.

Diesels pack more power than their gasoline counterparts. Drivers report their small cars are zippy and the engine remains popular in large and small trucks that require power.

In Europe, where pump prices are three times higher than in the United States, the diesel engine is under the hood of more than 50 percent of the cars.

But in the United States, the diesel retains a negative image of a clanking engine spewing sooty exhaust. It didn't help when in the 1980s General Motors produced a faulty diesel (its poorly designed engine block wasn't capable of withstanding extreme heat) and left consumers wary about the engine's worth in cars.

Growing market
Germany is the world leader in making quality diesels that more and more are finding their way into U.S. Today's diesels are much less sooty and noisy, and even the problem of cold weather starts is a thing of the past.

In the United States diesel vehicles account for 3.5 percent market share, mostly because of trucks. That's expected to grow to 5 percent by 2010. As Volkswagen struggles to keep up with demand for its Jetta TDI, other carmakers will join in: Mercedes, BMW, Audi, Nissan, Honda and Hyundai all have reported they will produce diesels for the U.S. market. Increased marketing will naturally focus more attention on diesel engines.

The hybrid car market is expected to continue growing with at least seven new models challenging Prius's dominance. J.D. Power foresees the gas/electric hybrid market to continue impressive growth to just under 5 percent of the U.S. market by 2010; it's at about 3 percent now.

Meantime, what's an environmentally conscious consumer to do?

Regardless of what's under the hood, the key is to buy small. Weight and engine size, combined with things like tire size (and pressure) and aerodynamics, determine how much energy is needed to get down the road. Big and bulky requires much more fuel, which is why large SUVs and the Hummer are considered eco scourges.

Both the hybrid and diesel qualify for limited tax breaks.

For in-city driving, it's tough to beat the hybrid. Sure, the technology is complicated, but favorable warranties show manufacturer confidence in their product (if you buy used, watch out for the replacement costs for batteries).

But if much of your driving is on the highway, the diesel is worth a look.