Nonrenewable energy is energy derived from sources that, for all practical purposes, cannot be easily made or renewed. Fossil fuels, which include coal, oil, and natural gas are considered to be nonrenewable energy sources because the rate of their formation is so slow on human timescales that they are effectively being used without any replenishment. Uranium (used in nuclear power) is also non-renewable, although its reserves are very large compared to its rate of use. Compare with renewable energy.