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