Below you can find some useful links:
Eurogas.org - European Union natural gas industries
Boostlpg.co.uk - English Association for LPG
WLPGA - World Association for LPG
AEGPL - European Associacion LPG
Prensavehicular.com - LATAM magazine for gas vehicles
Iea.org - International Energy Agency
ngva.eu - Natural Gas and Biogas Vehicle Association
ngvamerica.org - Natural Gas Vehicle America