*Coal bed methane recovery is reported to be 15–23% in China (14, 15); we take 20% as the average. Recoveries for advanced and best technologies are from
a US Environmental Protection Agency publication (16).
†
Data are from a study by Zhou (17).
‡
Data are from a report by the International Fertilizer Association (18), with advanced technologies being the world average and the best technologies being
those that operate at the highest energy efficiency.