Which of the following countries is not a member of OPEC?

Yemen is not a member of the Organization of the Petroleum Exporting Countries (OPEC). OPEC was established to coordinate and unify the petroleum policies of its member countries in order to secure fair and stable prices for petroleum producers, ensure a steady supply of oil to consumers, and provide a fair return on capital to those investing in the industry.

Countries like Saudi Arabia, Venezuela, and Iraq are founding and significant members of OPEC, playing vital roles in global oil production and influencing oil prices due to their substantial oil reserves. Yemen, on the other hand, has a smaller oil sector and has not been included in OPEC. Its oil production is limited compared to other member countries, which makes its exclusion from OPEC consistent with the organization's focus on larger oil-producing nations.