The highest profits were recorded in the resources, financial and service sectors.

Companies listed in the SET50 contributed 77 per cent of the aggregate net profit, while the remaining firms in the SET 100 added 5 per cent.

The companies at the top of the profit-making ladder were PTT Plc, Siam Cement Plc, PTT Exploration and Production Plc, Thai Airways International and Advanced Info Service.

SET executive vice president Suthichai Chitvanich said 482 of 504 firms listed both on the SET and in the Market for Alternative Investment, have submitted financial statements for the first three months of the year.

"The overall earnings of listed firms in the first quarter have improved from the same period last year, with higher net profits as well as sales," Suthichai said.

Of the 467 firms listed on the SET, 376 recorded net profits totalling Bt145 billion, up 8 per cent year on year. The total revenues of these firms was Bt1.24 trillion, an increase of 23 per cent year on year.

Of the 37 firms listed on the Market for Alternative Investment, 36 have submitted financial statements showing a combined net profit of Bt279 million, down 10 per cent year on year, while their total sales were Bt5.73 billion, up 14 per cent.

The SET said firms listed in the SET100 and SET50 recorded higher net profits mainly because of higher foreign exchange gains from the stronger baht.

PTT recorded the highest first quarter net profit, Bt23.72 billion; followed by Siam Cement Group, Bt9.55 billion; PTT Exploration and Production, Bt7.84 billion; Thai Airways International, Bt6.21 billion; and Advanced Info Service, Bt5.29 billion.

The SET said 425 listed companies in eight industrial groups accounted for Bt136.15 billion, or 94 per cent of the total net profits.

The resources sector yielded net profits of Bt43.8 billion, up 6 per cent year on year; the financial sector, Bt30.23 billion, about the same as last year; the services sector, Bt20.78 billion, up 30 per cent; the property and construction sector, Bt15.86 billion, down 27 per cent; and the technology sector, Bt12.81 billion, up 12 per cent.