IN JUNE 2008, Rick Ridgeway, the mountaineer and Patagonia Inc.'s vice president of environmental initiatives, arrived at the annual Western Governors' Association meeting in Jackson, Wyoming, armed with a slick slide show about "the most badass wolverine on the planet." Ridgeway's purpose was to convince the 14 governors and four Canadian premiers in attendance, along with 500 audience members, that wildlife corridors in the Rocky Mountain West badly needed political support. To make his case, he told the story of M3, a wolverine that was tracked traveling hundreds of miles between Glacier National Park and Alberta, climbing Montana's 10,466-foot Mount Cleveland on the way. Tom Brokaw introduced Ridgeway, the wolverine bit got a standing ovation (M3 had summited Cleveland in the deep snows of February, hanging out for an hour to enjoy the view), and Wyoming governor Dave Freudenthal gave Ridgeway a bear hug.

Afterwards, three representatives from BP America approached Ridgeway to ask how the company could participate. Since 2006, BP had been partnering with the Nature Conservancy (TNC) to mitigate the impacts of natural-gas drilling on sage grouse and pronghorn antelope corridors in Wyoming. "Rick's presentation moved me and spoke to some of what we were already doing," Lisa Hough, senior director of government and public affairs for BP America's Rockies region, told me recently. She then added, without a hint of irony, "It's what BP believes. To work in the community, you also need to protect the landscape."

That year, Ridgeway launched Freedom to Roam, a coalition that includes NGOs such as Defenders of Wildlife and the Wildlife Conservation Society, governmental groups like the Association of Fish and Wildlife Agencies, and businesses including Patagonia, Walmart, Southern California Edison, Microsoft, and BP. Looking back from the fouled beaches of 2010, this would seem an unfathomable alliance: Patagonia—a business so dedicated to sustainability that it eschews the notion of growth—and BP, a company so dedicated to profiteering that it brought about the partial death of a sea.

Of course, back in 2008, London-based BP was widely perceived as the greenest brand in oil. After assuming the now-mocked "Beyond Petroleum" tagline, in 2000, BP had invested some $4 billion in what it calls "low carbon" energy programs (remember actor Edward Norton's BP Solar Neighbors campaign?) and given millions of dollars to nonprofits, including TNC and Conservation International (CI). But in the wake of the Deepwater Horizon mess and BP's obfuscation—the barring of journalists from beaches, the gross underreporting of the size of the spill—you have to wonder whether it was all merely marketing spin. And you might also expect BP's new friends to drop the company like a hot coal. But just the opposite has happened: Green groups seem more determined than ever to engage Big Oil—which seems akin to asking your heroin dealer for cleaner needles following a nasty bout of hepatitis.

This raises an obvious question: Why?

IT'S WORTH REMEMBERING how we got here. The great new era of green cooperation began in 1990, when the Environmental Defense Fund helped McDonald's reduce the use of Styrofoam packaging. While groups such as the Sierra Club still stuck to their bread and butter—suing polluters—they added another tool to their belts: sitting down with corporations to work toward a specific goal. One example is the Energy and Biodiversity Initiative, which existed from 2001 to 2007 and saw CI, TNC, and Fauna & Flora International joining with BP, ChevronTexaco, and Shell to research Big Energy's impact on wildlife. Other alliances looked at the companies themselves. In 2008, Walmart partnered with Patagonia to overhaul its corporate philosophy. The retail giant now sells organic dairy products and Marine Stewardship Council–approved seafood. Its transformation has been held up as a model for dealing with the realities of development in a smart, nonreactive manner.

Even the combative Sierra Club came into the fold, endorsing a line of biodegradable Clorox bathroom cleaners called Green Works in 2008. Not surprisingly, such alliances have led to cries of selling out. The Sierra Club has received about $1.1 million so far from Green Works sales, CI has taken $1.63 million from BP since 2003, and TNC has accepted $7 million from the oil giant over the past 20 years. (Freedom to Roam is less expensive: Each corporate partner contributes $50,000 in membership dues.)

"If nonprofits took money from only 'good' companies, they'd be bankrupt," says Joel Makower, executive editor of GreenBiz.com and author of Strategies for the Green Economy. "That's not to say they should get in bed with every polluter on the planet. Somewhere in the middle is a good-faith partnership."