"Congress is considering proposals for market-based programs to limit greenhouse gas emissions. Many proposals involve creating a cap-and-trade program, in which an overall emissions cap is set and entities covered by the program must hold tradable permits-or "allowances"- to cover their emissions. According to the Congressional Budget Office (CBO), the value of these allowances could total $300 billion annually by 2020. The government could either sell the allowances, give them away for free, or some combination of the two.Some existing cap-and-trade programs have experience selling allowances. For example, member states participating in the European Union's (EU) Emissions Trading Scheme (ETS) have sold up to about 9 percent of their allowances, and the amount of auctioning is expected to increase significantly starting in 2013. In the United States, the 10 northeastern states participating in the Regional Greenhouse Gas Initiative (RGGI) have auctioned about 87 percent of their allowances.This report is part of GAO's response to a request to review climate change policy options. This report describes the implications of different methods for selling allowances, given available information and the experiences of selected programs..."