Determining how long fossil fuel reserves, the non-renewable sources of energy, will last is dependent on production rates and the rate of consumption. Other factors complicating the determination of how long fossil fuel reserves will last is whether additional supplies will be discovered, the economics of recovery of fossil fuels, and the growth of renewable sources of energy. Different models have been proposed, but researchers are now predicting that oil and gas reserves will last another 35 and 37 years, respectively. Coal reserves are predicted to last 107 years. Based on this model, coal will be the only fossil fuel available after 2042 and would last until 2112.