The cubic mile of oil (CMO) is a unit of energy. It was created by Hew Crane of SRI International to aid in public understanding of global-scale energy consumption and resources. Significant sources of energy include oil, coal, natural gas, nuclear, hydroelectric, and biomass (primarily the burning of wood). Other energy sources include geothermal, wind, photovoltaic, and solar thermal. The various energy units commonly used to measure these sources (e.g., joules, BTUs, kilowatt hours, therms) are only somewhat familiar to the general public, and their relationships can be confusing. These common energy units are sized for everyday activities (a joule is the energy required to lift a small apple one metre vertically). For regional, national, and global scales, larger energy units, such as