Economists often use the four-firm concentration ratio as a measure of the competition in a market for goods and services. When four companies gain a combined market share of 40 percent or higher, an oligopoly has formed. The prices offered to suppliers, the prices charged to consumers, and the wages paid to workers are no longer determined mainly by market forces. A handful of companies have gained control of the market. Effective government regulation becomes more difficult, as state and federal agencies readily become “captive” to the corporations they’re supposed to oversee.