(FORTUNE Magazine) – HONDA Location: Japan Year founded: 1945

REVENUE $84.2 Billion EMPLOYEES 145,000

The most fuel-efficient auto company in the U.S.

WHILE OTHER automakers gripe, Honda attacks the issues of fuel economy and emissions with relish. Working independently, it is focusing on three alternative fuel technologies: gas-electric hybrid, clean diesel, and fuel cell. Honda has also taken a crack at solving a problem other automakers have left to the oil companies: creating an infrastructure for hydrogen. Honda's solution is for individual refueling stations that provide heat and electricity for the home as well as hydrogen for a fuel-cell-powered car. Long term, Honda wants to be the world's cleanest, most efficient manufacturer. It has promised to reduce CO2 emissions from its factories as well as its vehicles by 5% between 2005 and 2010--on top of the 5% it achieved between 2000 and 2005.

CONTINENTAL AIRLINES Location: Houston Year founded: 1934

REVENUE $13.1 Billion

EMPLOYEES 44,000

Worked with Boeing to engineer more fuel-efficient aircraft

AMID RISING concern about aviation pollution, British Airways introduced a "CO2 emission calculator" on its website, letting passengers pay to offset the carbon dioxide generated by their flights. Lufthansa recently equipped an Airbus A340 with a 1.5-ton mobile laboratory to track gases and compounds. But it is American airline Continental that's gone furthest to green operations. Besides spending more than $16 billion over the past ten years to replace its fleet with more efficient aircraft, it installed fuel-saving winglets that reduce emissions by up to 5% on most of its Boeing 737s and 757s, and reduced the nitrogen oxide output from ground equipment at its Houston hub by over 75% since 2000. Its 13 full-time staff environmentalists work with engine manufacturers, design green terminals, and track carbon emissions and chemical recycling daily. Even all the trash from company headquarters is later sorted for recyclables.

SUNCOR Location: Canada Year founded: 1917

REVENUE $13.6 Billion EMPLOYEES 5,500

Measures the environmental impact of each project

FINDING black gold is a dirty job--particularly when it's buried in tar sands. But Suncor still stands out for how it does the job. Its environmental and social efforts have earned it membership in the Dow Jones sustainability index and the British equivalent, the FTSE4Good. In a survey of 23 global oil companies last year, Jantzi Research, a Canadian consultancy, named Suncor a top performer, noting its environmental and greenhouse-gas management programs. Specifically, it has improved emissions intensity (the amount of oil it extracts per ton of greenhouse gases emitted) 25% since 1990. Ditto for energy, sulfur dioxide,, and nitrogen oxide. Suncor is part of an initiative to develop carbon-capture techniques. And while Suncor hopes to double its production by 2012, its water management is so advanced that it expects to draw no additional water from Alberta's Athabasca River.

TESCO Location: Britain Year founded: 1919

REVENUE $71 Billion EMPLOYEES 380,000

Cut energy use and is trying to get customers to think green

WIND-POWERED stores, high-tech recycling, biodiesel delivery trucks--Tesco does all that. Last year the company pledged to cut the average energy use in its British buildings in half by 2010; now it says it will get there two years early. State-of-the-art trains that have lower-than-normal noise and pollution reduce the use of trucks, slashing thousands of tons of carbon dioxide emissions; in a major store initiative, Tesco will estimate the "carbon costs" of each item. To ensure that its leadership walks the talk, Tesco now determines senior-management bonuses partly on meeting energy- and waste-reduction targets. Tesco is also encouraging customers to be greener by awarding points, redeemable for merchandise, to those who bring their own reusable shopping bags.

ALCAN Location: Canada Year founded: 1902

REVENUE $23.6 Billion EMPLOYEES 68,000

Investing in clean, efficient manufacturing

WHEN ALCAN took over French rival Pechiney in late 2003, the Montreal-based aluminum maker also landed world-class smelting technology. Because of Pechiney's proprietary methods (and an aggressive push by Alcan to track emissions), the company has been able to reduce its greenhouse-gas output by 25% since 1990, while production increased 40%. Alcan's latest goal is to install a high-capacity process that increases energy efficiency by as much as 20% and lowers emissions. A pilot plant in Quebec is already testing the technology. "It's inherent to the engineering culture to respond to problems like these," says Alcan's Corey Copland. "It's what makes engineers tick."

PG&E Location: San Francisco Year founded: 1852

REVENUE $12.5 EMPLOYEES 20,000

Strategic investments in efficiency and renewables

PG&E PLAYED a big role in getting mandatory controls on greenhouse gases enacted last year in California, and CEO Peter Darbee is now pushing for federal legislation.

The utility generates 56% of its retail electricity sales from non-greenhouse-gas-emitting sources, and it aggressively helps customers become more efficient. For instance, it subsidizes homeowners who buy energy-efficient appliances with $75 grants. PG&E is also experimenting with a variety of clean power alternatives. It is seeking permission to develop generation projects that could convert wave energy off the Pacific Coast into electricity. It is bullish on solar thermal technology, and it has a pilot project in the San Joaquin Valley in which cow manure is turned into electricity. "That's a dung good idea," cracks Darbee.

Jokes aside, Darbee is seriously excited about the prospect of plug-in hybrids that would draw power from the electricity grid at night and then feed power back into the grid during the day when demand peaks. These clean cars would burn less gasoline, pollute less, and take advantage of the utility industry's capital-intensive infrastructure. "The energy industry," Darbee concludes, "is on the brink of a revolution."

S.C. JOHNSON Location: Racine, Wis. Year founded: 1886

REVENUE $7 Billion EMPLOYEES 12,000

Three generations of committed environmental stewardship

IN 1935, long before sustainability became a corporate buzzword, H.F. Johnson Jr. led a 15,000-mile expedition to Brazil in search of a sustainable source of wax, the carnauba palm tree, for his company's first product, Johnson's Wax.

His grandson and the current CEO, Fisk Johnson, has continued that legacy at S.C. Johnson, a family-owned company that makes Windex, Pledge, Ziploc bags, and Raid. Its most notable innovation is its Greenlist process, a classification system that evaluates the impact of thousands of raw materials on human and environmental health. By using Greenlist, S.C. Johnson eliminated 1.8 million pounds of volatile organic compounds (VOCs) from Windex and four million pounds of polyvinylidene chloride (PVDC) from Saran Wrap, which is now PVDC-free. (VOCs and PVDC are both pollutants.) The company licenses Greenlist royalty-free to other firms that want to use it. It is also cutting back its reliance on coal-fired power, recently building its own power plant that runs on natural gas and methane piped in from a nearby landfill. Glenn Pricket of Conservation International says that when it comes to the environment, "Fisk Johnson is probably the most personally committed CEO I've met."

GOLDMAN SACHS Location: New York Year founded: 1869

REVENUE $69.4 Billion EMPLOYEES 24,000

Bold climate-change policy shapes major investments.

WHEN GOLDMAN SACHS announced a groundbreaking environmental policy in 2005, critics said chief executive Hank Paulson was imposing his green ethos. Wrong. The bank has become even more planet-friendly since Paulson left. Why? Because it is doing lots of green business.

Goldman's investment of $1.5 billion in cellulosic ethanol, wind, and solar have paid off. Texas Pacific and Kohlberg Kravis Roberts turned to Goldman, which had built bridges to environmental groups, as they prepared a bid for Texas energy company TXU. Research clients are pleased that Goldman's equity analysts in Europe now factor environmental, social, and governance issues into their reports. "The world's changing," says one Goldman official. The company is too--some cars that take bankers home are hybrids.

SWISS RE Location: Switzerland Year founded: 1863

REVENUE $24 Billion EMPLOYEES 10,500

Developing financial tools to deal with the risks of climate change

SWISS RE'S main product is insurance for insurers, so its products never come near a smokestack. And Swiss reinsurance companies are not exactly known for boldness. Even so, Swiss Re has been way ahead of the pack on climate change, warning as early as 1994 about the bottom-line threat in the form of higher claims from storms and other weather-related disasters.

In addition, Swiss Re has pioneered products like weather-based derivatives to hedge these risks. Buyers can bet on future heat waves or cold snaps with puts and calls on specific periods of time and temperatures, much as conventional options have a preset strike price for a stock. So a farmer in India might be able to buy insurance from a local insurer in case the usual monsoon rains fail to arrive or, conversely, his fields are flooded. Swiss Re was also among the early supporters of the Chicago Climate Exchange, an emerging hub for traders in derivatives linked to carbon emissions.

HEWLETT-PACKARD Location: Palo Alto Year founded: 1939

REVENUE $91.7 Billion EMPLOYEES 156,000

Silicon Valley's longtime industry leader in eco-sensitivity

HIGH TECH is falling all over itself to go green. It may be that Prius-driving engineering types are more eco-sensitive than the rest of us, or maybe they're simply battling for competitive advantage. The fact is, as more of modern life goes digital, the environmental impact of those computers and gadgets has gone from negligible to considerable. Hewlett-Packard has done the most to mitigate that. HP owns massive e-waste recycling plants, where enormous shredders and granulators reduce four million pounds of computer detritus each month to bite-sized chunks--the first step in reclaiming not just steel and plastic but also toxic chemicals like mercury and even some precious metals. HP will take back any brand of equipment; its own machines are 100% recyclable. It has promised to cut energy consumption by 20% by 2010. HP also audits its top suppliers for eco-friendliness, and its omnibus Global Citizenship Report sets the standard for detailed environmental accountability. SOURCES: DEPARTMENT OF ENERGY; EIA; CERES; ARON CRAMER; BUSINESS FOR SOCIAL RESPONSIBILITY; DAN ESTY; JONATHAN LASH, WORLD RESOURCES INSTITUTE; MATTHEW KIERNAN, INNOVEST STRATEGIC VALUE ADVISORS; FRED KRUPP, ENVIRONMENTAL DEFENSE; JOEL MAKOWER, GREENER WORLD MEDIA; KLD RESEARCH; NATURAL RESOURCES DEFENSE COUNCIL; GLEN PRICKET, CONSERVATION INTERNATIONAL; ANDREW SAVITZ

Alex Taylor III, Marc Gunther, Jia Lynn Yang, Matthew Boyle, Cait Murphy, Barney Gimbel, Oliver Ryan and Nelson D. Schwartz contributed to this article.