Which organization controls over 40% of the world's oil supply?

The Organization of the Petroleum Exporting Countries (OPEC) is a key player in the global oil market, as it is responsible for coordinating and unifying the petroleum policies of its member countries. OPEC was established to ensure the stabilization of oil markets, so its member nations can ensure fair and stable prices for petroleum producers and a regular supply for consumers.

OPEC controls a significant portion of the world's oil supply—over 40%—because it consists of some of the largest oil-producing nations, primarily from the Middle East, Africa, and South America. This control allows OPEC to influence oil prices significantly through production quotas and agreements, which can affect global economies.

In contrast, organizations like the International Monetary Fund (IMF) and the World Bank focus on financial stability and economic development rather than oil production and pricing, and the United Nations Environment Programme (UNEP) concentrates on environmental issues rather than the management of oil resources. Thus, OPEC is the correct answer, as its role directly relates to the management and control of oil supply on a global scale.