BG Group has sold a quarter of its massive Queensland Curtis LNG project to China's CNOOC for $1.9 billion, while providing a downbeat assessment of its oil and gas production for 2013.

The sale will increase the interest of the China National Offshore Oil Corporation (CNOOC) in the first of two "trains" or liquefaction units to be built on Curtis Island at Gladstone, from 10 per cent to 50 per cent – effectively a quarter of the LNG project.

CNOOC will also take a 25 per cent stake in certain Bowen and Surat Basin fields, which will supply coal seam gas to the LNG plant.

BG also announced a new gas sale to CNOOC, 5 million tonnes a year, partly supplied by the Queensland Curtis LNG project, which is being managed by BG's Australian subsidiary QGC as operator and majority owner.

Advertisement Announcement of the sale came as BG reported its September quarter earnings, which triggered a 14 per cent drop in its share price – a record one-day fall for the stock - after chief executive Frank Chapman said production would be flat next year.