Final answer:
Venezuela has the world's largest oil reserves and is a member of OPEC. Despite Saudi Arabia's significant role as a key exporter and OPEC member, Venezuela holds the title for having the largest reserves, including heavy oil.
Step-by-step explanation:
The country with the world's largest oil reserves and a member of the Organization of Petroleum Exporting Countries (OPEC) is Venezuela. While Saudi Arabia has been the world's leading oil exporter and a key OPEC member, holding over 20 percent of the known oil reserves, it is Venezuela that claims the title for the largest oil reserves as of the data available.
The distribution of proven oil reserves shows that much of it is located in the Middle East and certain OPEC member countries, including Venezuela, which has heavy oil that is harder to extract and process compared to the light oil characteristic of the Middle East.
OPEC is an influential organization that seeks to maximize profits for oil-exporting countries and has historically influenced global oil prices through their collective decisions on oil production and exports. The power of OPEC was demonstrated during the energy crisis of the 1970s and continues to affect the global oil market.