At noon, the index lost 16.47 points or 1.24 per cent to 1,317.10 points, on turnover of Bt17.6 billion.
On Monday, US benchmark West Texas Intermediate crude sank 5.8 per cent and Brent shed 5.3 per cent - hitting levels not seen since February 2009. WTI tumbled 2.7 per cent and Brent lost 1.9 per cent Friday.
In China, data showed that China's exports fell by a more-than-expected 6.8 per cent in November from a year earlier, their fifth straight month of decline.
Shares in China, Hong Kong and Japan ended lower today.