Edited sentence: " According to the EPA, two-stroke cycle engines can "cause more pollution in two hours than a car running for an entire year.According to the Sierra Club, The small, inefficient two-stroke cycle engines of some of these machines spew out as much as 30 percent of their fuel unburned – polluting the soils, air, and water of our National Forests, National Parks, and other public lands.Because fuel leaks through the exhaust port each time a new charge of air/fuel is loaded into the combustion chamber, oil pollution is a problem at many National Parks and outdoor recreation areas that allow ORVs.Because some four-wheelers, snowmobiles, dirt bikes, and small watercraft use a two-stroke cycle engine, the U.Environmental Protection Agency considers them to be a potentially significant source of nonpoint source pollution or "pollution runoff.For example, one jet-ski driven for one 8 hour period emits the same amount of pollution as a car driven for 100,000 miles.To address these problems, some organizations have begun to offer biodegradable two-stroke engine oil, and newer models are said to be more efficient