Other commentators have pointed out that China has been taking a role as a leader in making use of coal as an electricity source more clean and responsible. For instance, the country built new ultra-supercritical coal plants (~44% efficiency) before the United States.[66] While the average efficiency of the coal fleet in China remains less than that of the US, the gap is quickly closing. In 2009, China required companies building new plants to retire an old plant for every new one built.[67]