The top 5% of companies by revenue account for 85% of Thailand's business sector revenue, while medium-sized companies have been restricted in funding accessibility and small firms have low productivity, according to the Bank of Thailand's think tank.
Revenue concentration of these large companies has lingered for more than 10 years, said Archawa Paweenawat, principal researcher of the Puey Ungphakorn Institute for Economic Research (Pier).
Moreover, these large companies enjoy a 46% share of sales and 60% share of profit among all Thai business operators, Mr Archawa said.
The top 5% by revenue this year are in wholesale, retail, auto manufacturing and oil refining, he said.
The finding is part of a study of Thailand's business structure using 750,000 companies' financial statements over the course.
Medium-scale firms managed to yield higher return on investment than large companies, but their lending accessibility is limited, Mr Archawa said.
Both medium-sized and small companies have problems in current asset management, he said.
The study found that the power of companies with high market influence has increased at a faster pace than for others.
Companies in the service sector have superior market power than those in the manufacturing sector, Mr Archawa said.
The country's top 5% of companies by market influence are engaged in retail, wholesale, restaurants, hospitality and food manufacturing.
Operators in water transport, travel agencies, warehouses and entertainment have significantly increased in market power, while those in telecom, printing, sport/recreation, information technology and restaurants have seen their market influence decline.
Market power has an adverse impact on efficiency in resource allocation, discouraging investment to improve productivity and weakening motivation and exportability.
A continuous decline in the business dynamics of Thai companies has raised their average age, and there is a correlation between zombie companies and business dynamics.
Zombie companies are unprofitable companies that are kept alive.
Industries that have a high number of zombie companies include construction, hospitality, sport/recreation, education and basic metal production, Mr Archawa said.
The continuous fall in Thai business dynamics and the persistence of zombie companies will narrow the chances of newcomers entering the market and bode ill for the growth of other firms engaged in the same industries, so policies to accelerate wiping out these zombie firms and to ease the entry of new players are required.