While alternative automotive fuels are being produced and used at a record pace, alternative jet fuels are not receiving the same amount of attention. While it is not as obvious as pulling up to the pump every few days, increasing gas prices are having a significant impact on airline ticket prices. Both government and corporate researchers are investigating alternative fuels for commercial jet engines, but widespread use seems to be decades away. One major obstacle faced by alternative jet fuels is the harsh conditions they are transported and used in, and for now alternative jet fuels are currently more expensive than traditional ones. Most commercial airplanes use a form of light kerosene, which is heavier than gasoline but lighter than diesel fuel. One alternative under investigation is biodiesel, but it freezes at a much higher temperature than the traditional jet fuel, which is a problem when considering the temperature at 35,000 feet. Scientists are working on ways to keep the fuel from freezing easily. Just like in automotive applications, we are likely to see blends of biodiesel and jet fuel appear first. Hydrogen is an other alternative, which would require little modification to the jet engine, but just as is the case with cars, storage is a major issue. One other concern is the amount of water produced by a hydrogen burning jet engine. While in cars the water is released close to the surface, at altitude, the hydrogen burning jet engines could become a cloud-making machine, the impact of which is unclear.