Singapore is the best place in the world to carry out business but significant barriers remain in the rest of the ASEAN region, a study released in Vietnam on Thursday said.
The World Economic Forum index ranked 125 countries based on their performance in four main areas: market access, border administration, transport and communications infrastructure and general business environment.
Singapore kept the top rank it held in last year's study, but five other members of the Association of Southeast Asian Nations (ASEAN) fell.
Vietnam improved from 89th to 71st largely because of its accession to the World Trade Organization three years ago, Thierry Geiger, a co-author of the study, told a news conference.
But he said barriers to trade in ASEAN "remain many and significant", primarily in border administration and transport infrastructure.
The study said Malaysia "stands out positively" at 30th position, compared with 28th last time, while Thailand is at 60, down from 50 a year ago, and Indonesia ranked 68th, from 62nd.
The Philippines sunk to 92 from 82, and Cambodia hit a "very low" 102, down from 92, the study said.
Data from ASEAN's other members, Laos, Brunei and Myanmar, was not included in the study.
ASEAN is working towards establishing by 2015 a single market and manufacturing base of about 600 million people.
The World Economic Forum, a Geneva-based independent organisation, released the study ahead of its World Economic Forum on East Asia in Ho Chi Minh City from Sunday.