Power plants are almost exclusively small two-stroke internal combustion engines, between 80 cc and 350 cc, that burn a mixture of gasoline and oil. These engines are favored for their quick high r.p.m. thrust and low weight, using approximately 3.7 litres (1 US Gal.) of fuel per hour depending on paraglider efficiency, the weight of unit plus pilot, and flying weather conditions. At least one manufacturer is producing a 4-stroke model favored for its strong lower r.p.m. thrust and better fuel efficiency.