the green issue, Earth Day 2008.(News)

Oil tankers sailing from the OPEC states to America filled with $100 barrels of petroleum are doing what decades of screeching environmentalists failed to do, bringing the virtues of fuel economy and efficiency home to consumers in the world's biggest, richest car market. Sales of big personal-use trucks are sagging, and those of small cars are booming again. To be sure, environmental urges, particularly rising social awareness about the issue of climate change, play a role in consumer attitudes, but it's hard to argue with economics as a motivator.

If we define the green segment as those people willing to pay more-not just those who say they'd like a cleaner, more efficient car if it didn't cost them any coin, convenience or comfort-the truly committed environmentalist sector amounts to the same 3 to 5 percent of the market as it did 10 or 20 years ago. (That's about the same size as the enthusiast sector, defined as those willing to pay more for performance, by the way.) The greens find more options today, though, now that their interests align with pocketbook issues and even those patriotic visions of increasing the nation's independence from foreign sources of energy.

Economics propels not just the consumer but governments and business as well. Initiatives that were deemed good ideas but went nowhere before have a sense of urgency about them now, whether you're talking about cleaning up your industrial processes or raising fuel-economy standards. Price volatility in the oil sector opens the door for venture capitalists who see opportunity today where the prospects for alternative fuels just didn't pencil out when oil went for $30 a barrel. Government incentives to pursue these ideas grow more abundant.

On the following pages, you'll read about alternatives to traditional gasoline-fueled ...