The market for renewable energy certificates in Europe is young but promising. Despite being a voluntary market with only 16 member states actively involved, there are over 140 counterparties trading green certificates. Some 66 million certificates (each representing one megawatt-hour of renewables-sourced power) were issued in 2006, a number that is expected to rise to 100 million for 2007. Of these, 25 million are expected to be traded internationally between the 16 participating member states