1. Statistical Review of World Energy;BP,2007
2. The competition between coal and natural gas;Ellerman;Resources Policy,1996
3. US Crude Oil, Natural Gas, and Natural Gas Liquids Reserves 2004 Annual Report;Energy Information Agency,2005
4. Annual Energy Outlook;Energy Information Agency,2006
5. Additions to Capacity on the US Natural Gas Pipeline Network 2005;Energy Information Agency,2006