China Oilfield Services' (HKG:2883) controlling shareholder, China National Offshore Oil, is planning to invest between 300 million yuan and 500 million yuan to increase its shareholding in the company within the next 12 months, a Wednesday filing with the Hong Kong bourse said.

China National Offshore Oil currently holds 2,410,849,300, or 50.53% shares in the oilfield surveying services company. This comprises 2,410,847,300 A shares and 2,000 H shares.