Combined-cycle electric generating systems are combustion and steam turbines that operate in groups commonly referred to as power blocks. Since 2014, the average size of a natural gas-fired combined-cycle power block has increased significantly. The average combined-cycle power block installed between 2002 and 2014 was about 500 megawatts (MW). After 2014, power block capacity increased, reaching an average of 820 MW in 2017. Power blocks have increased in size as the performance of combined-cycle units has continued to improve, and current and projected natural gas prices and supply provide a competitive advantage for the combined-cycle technology. The most common configuration involves two combustion turbines supporting one steam turbine.