The Energy Institute (EI) is a professional organization for engineers and other professionals in energy-related fields. The EI was formed in 2003 by the merger of the Institute of Petroleum (dating back to 1913) and the Institute of Energy (dating back to 1925). It has an international membership of about 20,000 people and 200 companies. Its main office is at 61 New Cavendish Street, London. EI is a registered charity with a Royal Charter.