BEIJING, Aug 28 (Reuters) - Chinese offshore oil and gas major CNOOC posted record first-half profit on Thursday, boosted by output growth and higher oil prices.

Net profit attributable to shareholders rose 25% to 79.73 billion yuan ($11.19 billion), CNOOC said in a filing with the Hong Kong Stock Exchange.

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CNOOC's net production of oil and gas increased by 9.3% to 362.6 million barrels of oil equivalent as it expanded its reserve base.

Key discoveries during the reporting period included Lingshui 36-1 in the South China Sea, its first ultra-deepwater gas field, and the Bozhong 26-6 and Penglai 9-1 oilfields. Overseas, CNOOC announced a more than 100 million metric ton oil and gas discovery at the Bluefin field at the Stabroek block in Guyana.

The Enping 21-4 oilfield set records for offshore drilling depth, CNOOC added. Well depth there exceeded 9,500 metres, the company said in June.

The value of its oil and gas sales jumped 22% to 185.11 billion yuan. Revenue in the six months to June 30 was 226.8 billion yuan, up 18% from the same period last year.

The company reported production costs for the period at $27.75 per barrel of oil equivalent, down from $28.20 in the first half of 2023.

CNOOC also said it would issue an interim dividend of 0.74 HKD ($.095) per share, inclusive of tax, a record high for the company.

(Reporting by Colleen Howe in Beijing and Chen Aizhu in SingaporeEditing by David Goodman)