Which of the following countries is a member of OPEC?

Ecuador's membership in OPEC, the Organization of the Petroleum Exporting Countries, highlights its role as a significant oil-producing nation. OPEC was established to coordinate and unify the petroleum policies of its member countries to secure fair and stable prices for petroleum producers and a regular supply for consumers. Ecuador has been a member of OPEC at different points in its history, contributing to the organization's goals of regulating oil production and prices to stabilize the market.

Understanding the context of the other countries is important for clarity. Brazil, while a notable producer of oil, is not a member of OPEC. Norway, although an important oil producer, operates outside OPEC, focusing on its own national policies and practices regarding oil production. Mexico, despite being a significant oil exporter, has also chosen not to join OPEC, pursuing its own energy policies independently. Thus, Ecuador stands out as the only country from this list that has actively participated as a member of OPEC.