There are two main sources of energy: conventional and non-conventional. Conventional sources include wood, flowing water, and fossil fuels like coal, petroleum, and natural gas. Non-conventional sources consist of solar, wind, biomass, ocean, geothermal, and nuclear energy. Various institutions collect data on worldwide energy consumption and production. Energy policy governs a country's approach to energy development, production, distribution, and consumption through legislation, treaties, and economic incentives and disincentives. A country's energy policy establishes goals for self-sufficiency, future energy sources and consumption, environmental standards, and mechanisms to implement the overall policy.