The supply of most natural products is limited; in recent decades, there have been some shortages. Often only a few large firms produce particular natural products, and in some countries those producers have been nationalized. These supply conditions give producers the power to limit supplies and administer prices, as with the Organization of Petroleum Exporting Countries (OPEC). Such supply conditions encourage processors and manufacturers to seek ways to ensure adequate supplies for the future by negotiating long-term purchase contracts (often at premium prices) or by purchasing the raw materials sources. For example, many large steel manufacturers own iron ore mining and processing operations