Charoen and Chaleo have grown richer from the previous year, while Dhanin and his family's net worth remains unchanged.

At the age of 62, Charoen, whose businesses ranges from property and hotels to liquor production, is ranked the 264th richest, with a combined net worth of US$3.4 billion (Bt119.3 billion), up from $3.2 billion the previous year.

Chaleo, 75, the owner of Red Bull energy drink, is ranked 279th with a net worth of $3.1 billion, up from $2.5 billion.

Dhanin, 67, whose family holdings are in agrobusiness, is ranked 390th, with net worth of $2.4 billion.

Topping the 2007 billionaire list remain super-rich Americans Bill Gates of Microsoft and Warren Buffet, both of whose net worth exceeds $50 billion.

"It has been a busy year in the fortune-hunting business," Forbes declared. "Strong equity markets combined with rising real estate values and commodity prices pushed up fortunes from Mumbai [Bombay] to Madrid. Forbes pinned down 946 billionaires, including 178 newcomers and 17 people who climbed back into the ranks after being absent for a year or more.

"Two-thirds of last year's billionaires are richer. Only 17 per cent are poorer, including 32 who fell below the billion-dollar mark. The billionaires' combined net worth climbed by $900 billion to $3.5 trillion. That equates to $3.6 billion apiece."

Forbes' annual billionaire list was announced on the same day that the International Labour Organisation (ILO) revealed a study that shows low-income workers in Thailand are earning less and having to work longer hours: many face increasing debt and there is growing disparity between the poor and the rich.

Titled "Reconciling Work and Family: Issues and Policies in Thailand", the study finds that changes in the labour market have put more strain on the working poor who do not earn a living wage. They are working long hours and often earn less than the minimum wage. Women at the same time are expected to do all the housework and look after the family. Grandparents are often called upon on take care of grandchildren and there is little support for childcare and elderly care.

"The time-money squeeze between family care responsibilities and the demands of work continues to be a challenge worldwide," said Nelien Haspels, ILO senior specialist in gender and women workers' issues. "Parents need reasonable working hours and a living wage, they need leave time that allows them to see their children and care for sick dependants without jeopardising their employment, and they need childcare facilities and services."