About 90% of beach land in Phuket is controlled by foreigners through Thai nominees, a leading research body has found.
A similar situation exists in other prime tourism destinations in provinces such as Chiang Mai and Rayong.
Local officials and legal experts have helped clear the way for foreign investors to take control of the country's rice farms and property in resort provinces, according to research on foreign land ownership by the Thailand Research Fund.
TRF called a seminar on the research findings yesterday attended by economics and legal scholars.
There recently has been speculation that foreign businessmen, particularly from the Middle East, were snapping up rice fields in the central plains and elsewhere through proxy local companies.
Transnational business consortiums were said to be holding the land through Thai nominees, which is against the law.
Some farmers are leasing land they previously owned but have since sold to the foreigners' proxy firms, observers said.
Siriporn Sajjanont, from the economics faculty at Sukhothai Thammathirat Open University and a member of the research team, said the study showed many kinds of property had been bought by foreigners through Thai nominees.
"About 90% of land along the coastline in Phuket is controlled by foreigners through Thai nominees," she said.
Foreign investment capital was essential for developing Phuket and Samui, as Thais do not have enough money to invest themselves, Ms Siriporn said.
The coastal areas most sought after by foreign investors were Pattaya in Chon Buri, Koh Phangan and Koh Samui in Surat Thani, Phuket and Hua Hin in Prachuap Khiri Khan.
In Chiang Mai, foreigners had used legal loopholes to exceed the limit on sales of condominium units, Ms Siriporn said.
There was evidence they hold the property through Thai nominees by marrying Thais. In some cases, Thai women were asked to register the foreigners' property in their own names.
The study found similar problems in Rayong involving foreign landholdings through Thai nominees with foreigners marrying Thais.
In some land lease cases, the period of leasehold was unusually long, Ms Siriporn said. The study found that some lease contracts stated the leasehold was "for life".
Land ownership by foreigners had been made possible by their Thai lawyers who had found legal loopholes to clear the way for foreigners to take control, the research found.
Village heads also had acted as land brokers to arrange sales of state land given to local people so they could make a living, the panellists said.
Village heads were close to residents and knew which prime land was available.
Some legal entities had been set up with 51% of shares held by Thais, although those Thais turned out to be mere legal advisers for foreigners and had no power to run the legal entities, Ms Siriporn said.
"We also found the same people had set up many entities," she said.
Some entities' regulations on shareholding structures allowed foreign shareholders more power than Thais in running those entities.
Col Surin Pikulthong, president of the Community Organisations Development Institute, said he had received information that Hmong people in the US had provided financial support for Hmong in Nan province to buy land and grow rice for shipment to the US.
Silaporn Buasai, vice-president of the institute, said she had heard that investors from Taiwan had bought land here for growing oranges to be sold in Taiwan.
Wichian Phuanglamjiak, vice-president of the Thai Rice Growers' Association, said rice farmers held additional information on land grabs by foreign investors.
He said the problem had remained unaddressed for too long and no state agency had taken the matter seriously.
Mr Wichian said farmers were pinning their hopes on the Department of Special Investigation to pursue the matter.
DSI investigator Pakorn Sucheevakul on Saturday said the agency was investigating four Thai companies in Ayutthaya which own rice farms of almost 10,000 rai.
Malee Antasin, 59, a farmer in Ayutthaya's Bang Ban district, said businessmen had bought many plots in her village since 1995.
She said she had felt "besieged" and pressured to sell her rice plot as her land had been enclosed by other plots owned by those investors. She was now taking the matter to court.