The Organisation of Petroleum Exporting Countries crude oil basket price has tumbled to a two-year low of US$18.50 a barrel in early London trade last night, putting pressure on the bottom-lines of China's big oil trio. Opec's lack of action to reduce output and weakening global demand has seen oil prices slump from about US$24 a barrel before the September 11 terrorist attacks. Under an informal Opec price stability mechanism, if the basket price (derived from prices of various countries) is less than US$22 a barrel for 10 consecutive trading days, Opec can call for a 500,000 barrels per day supply cut to bring it back to a US$22 to US$28 range. Opec is reluctant to cut output as a prop for oil prices which may deter efforts to revive a global economy weakened by the terrorist attacks. Opec ministers are due to meet on November 14 to discuss global oil supply. A survey by European brokerage ABN Amro found 20 leading banks and consultancies had a consensus oil price forecast of US$25.40 a barrel this year and US$21.30 a barrel next year. Analysts have recently downgraded earnings forecasts on PetroChina, China Petroleum and Chemical (Sinopec) and CNOOC. US brokerage Goldman Sachs slashed its estimated net profit on PetroChina 51 per cent to 17 billion yuan (about HK$15.9 billion) for next year, Sinopec 34 per cent to 8.8 billion yuan and CNOOC 38 per cent to 4.9 billion yuan.