Energy sources are of two categories, renewable and non renewable.
Non renewable resources include fossil fuels (petroleum, natural gas, coal) and nuclear fuel (mostly uranium, which is in limited supply). Use of both of them causes pollution. Fossil fuel cause oil spills, acid rain, air pollution, water pollution etc. Nuclear energy may give rise to radiation pollution.
Renewable resources of energy include biomass energy and some forms of inexhaustible energy like solar energy, hydro power, wind power etc. They are less polluting but far more expensive due to technological incipiency.