Dirty Thirty ranks the least efficient among the biggest carbon dioxide (CO2) emitters and finds that 27 of the 30 dirtiest power plants are coal-fired, with Agios Dimitrios in Greece, Frimmersdorf in Germany, and Aboño in Spain heading the WWF table...19 of the 30 plants analyzed are run by RWE (German), Vattenfall (Swedish), Enel (Italian), Endesa (Spanish), E.ON (German), and EDF (French).