The Prius G gets 44 mpg instead of 29 mpg. With gas prices at $3/gallon, it cost $2.70 to save an imported gallon with a hybrid compared with $7.20 with corn ethanol. They get their power from gasoline but use an electric motor to supply most or all of the power to the wheels. The simplest hybrid would work like this:

A battery runs the motor that drives the car.

A small gas engine powers a generator which charges the battery.

This is efficient because the gas engine runs under ideal conditions--the right speed and the right load. This saves all the gas wasted when sitting at stop lights, stepping hard on the gas pedal, or driving too fast or slow for the gear you are in.

Good hybrids also generate electricity from the car's own motion when you brake to a stop. This is free energy that is usually wasted heating up the brake drums.

Compared with all-electric cars, hybrids have a great advantage. You don't have to wait for them to charge. You just buy gas when you run out. With the same size gas tank, they go even further than a regular gas car.

This is a tough question, but it is the question we need to ask of all approaches to energy independence or CO2 reduction. For reference, ethanol costs over $7 per gallon saved in subsidies to corn farmers and ethanol producers (mostly producers).

Hybrids do better. A Toyota Prius hybrid would save fossil gallons at a cost of about $3/gallon. To be specific, if you own one for five years, you will save 882 gallons of gas and it will cost you $2,744 dollars more than if you bought a Toyota Corolla LE non-hybrid and drove the same 75,000 miles.

That's right. It costs more, even though you buy less gas, because the cars cost more. This is based on a cost study by Consumer Reports, which includes initial cost, depreciation, insurance, maintenance, financing and resale. It also assumes an average price of gas over the five years of $2.58.

The $3/gallon figure is without any federal subsidy. With the subsidy of $3,150 they assume in their April 2006 article, you would actually come out ahead. It would cost you less than nothing to save the 882 gallons of gas.

Although saving gas with hybrids is not yet cheap, the technology is doing very well considering how new it is. Toyota says it wants to be selling a million hybrids a year by 2012, and that it will need to bring the price difference down to a mere $1000 (instead of, say, the $5,600 difference on the Prius. If it did that, saving fossil gallons would cost less than nothing.