According to the Kentucky Clean Fuels Coalition, Mammoth Cave National Park is the first national park in the country to be 100% alternatively fueled.  That is, Mammoth Cave is numero uno out of 385 national parks. 

To service its 52,830 acres of land and its 81 permanent employees, as well as park visitors, Mammoth Cave has 21 E10 fueled vehicles, 22 E85 vehicles, 12 Biodiesel (ferries, backhoe, mowers), 2  electric vehicles, and 7  propane buses.