Title IV of the 1990 Clean Air Act Amendments created a market for trading sulfur dioxide (SO2) emission allowances among electric utilities. This trading system allows companies to save money by buying and selling the right to emit SO2. A study found that the cost of reducing SO2 emissions has decreased by over 50% since 1985, mainly due to using low-sulfur coal and technological improvements. While allowance trading can save $700–$800 million per year compared to strict regulations, most of these savings were not realized in the first two years of the program.