At least US$5trn is available for investment in the Greater Mekong Sub-region (GMS) countries (China, Vietnam, Thailand, Laos, Cambodia and Burma) if good opportunities are presented, state media reported, citing comments made by experts from the Asian Development Bank on the eve of the GMS summit. Prime ministers of the six GMS member countries will gather today and Tuesday to review the progress of co-operation and discuss how to improve the investment environment.