In recent years, U.S. natural gas combined-cycle (NGCC) electric generating capacity has increased as a result of relatively low natural gas prices and improved thermal efficiency and economies of scale from advances in turbine design. Newer turbines are more efficient than older turbine technologies, making them more cost-effective to run. As a result, the average annual capacity factor, or utilization rate, for newer NGCC generators in the United States is slightly higher than that of older, less efficient generators.