The OPEC Statute stipulates that: "any country with a substantial net export of crude petroleum, which has fundamentally similar interests to those of Member Countries, may become a Full Member of the Organization, if accepted by a majority of three-fourths of Full Members, including the concurring votes of all Founder Members".

The Statute further distinguishes between three categories of membership: Founder Member, Full Member and Associate Member.

Founder Members of the Organization are those countries which were represented at OPEC's first Conference, held in Baghdad, Iraq, in September 1960, and which signed the original agreement establishing OPEC.

Full Members are the Founder Members, plus those countries whose applications for Membership have been accepted by the Conference.

Associate Members are the countries which do not qualify for full membership, but which are nevertheless admitted under such special conditions as may be prescribed by the Conference.