Proven reserves (also called measured reserves, 1P, and reserves) is a measure of fossil fuel energy reserves, such as oil reserves, natural gas reserves, and coal reserves. It is defined as the "of energy sources estimated with reasonable certainty, from the analysis of geologic and engineering data, to be recoverable from well established or known reservoirs with the existing equipment and under the existing operating conditions." A reserve is considered proven if it is probable that at least 90% of the resource is recoverable by economically profitable means