American Petroleum Institute
www.api.org
Clean Energy Fuels
www.cleanenergyfuels.com
EIA – U.S. Energy Information Administration
www.eia.gov
Eurogas – The European Union of the Natural Gas Industry
www.eurogas.org
IEA – International Energy Agency
www.iea.org
IGU – International Gas Union
www.igu.org
World Energy Council WEC
www.worldenergy.org/wec-geis