In the 1960s a series of mergers saw coal production shift from small, independent coal companies to large, more diversified firms. Several oil companies and electricity producers acquired coal companies or leased Federal coal reserves in the west of the United States. Concerns that competition in the coal industry could decline as a result of these changes were heightened by a sharp rise in coal prices in the wake of the 1973 oil crisis. Coal prices fell in the 1980s, partly in response to oil price movements, but primarily in response to the large increase in supply worldwide which was brought about by the earlier price surge. During this period, the industry in the U.S. was characterized by a move towards low-sulfur coal.