The use of hybrid cars is one of the many "greening" efforts at Yellowstone National Park.

In 1997, when Yellowstone National Park celebrated its 125th anniversary, one of the questions asked was what can we do to preserve and protect this national treasure for the next 125 years? The result was “The Greening of Yellowstone.” Some “green” projects had already begun, such as demonstrating the cleanliness and efficiency of biodiesel fuel. Since that time the park and various partners have addressed a wide variety of pollution prevention, waste reduction, alternative fuels, and recycling projects. Together they have increased effective environmental conservation in the park and surrounding communities.