<em>The purpose of OPEC for members is to coordinate and unify the petroleum policies of its Member Countries and ensure the stabilization of oil markets in order to secure an efficient, economic and regular supply of petroleum to consumers, a steady income to producers and a fair return on capital for those investing in the petroleum industry.</em>
OPEC has been gaining steady power and influencing the global oil market since the 1970s when OPEC had ~50% of market share in global crude oil production. High market share has also given OPEC the bargaining power to price oil above what prices would be in a more competitive market.
