By Sam Li and Chen Aizhu

Aug 27 (Reuters) - Chinese offshore oil and gas major CNOOC 0883.HK 600938.SS posted a 13% decline in interim net income after lower oil prices offset the impact of record-high oil and gas production.

Net profit attributable to equity shareholders dropped to 69.5 billion yuan ($9.7 billion) after a record interim profit in 2024, according to a filing to the Hong Kong Stock Exchange.

Domestic peer PetroChina reported a 5.4% decline in net earnings to around $11.7 billion, while Sinopec's sank 40% to $2.99 billion.

CNOOC's net production of oil and gas increased 6% to a record 384.6 million barrels of oil equivalent during the period, with gas up 12% year-on-year.

"We steadily promoted construction of major projects and achieved record-high oil and gas production," CNOOC said.

It said reserve utilisation and recovery rates had improved, while the natural decline rate of producing oil and gas fields offshore China continued "at a low level".

CNOOC made five discoveries offshore China, including Jinzhou 27-6 in the northern part of the Bohai Sea, and successfully appraised large and medium-sized oil and gas bearing structures, including like Qinhuangdao 29-6, also in the Bohai Sea.

The company commenced production at Bozhong 26-6 oilfield Phase I off north China's Bohai Bay, the Buzios-7 project and the Mero-4 project in Brazil, as well as phase 2 of the Shenhai-1 deepwater gas project in the South China Sea.

Beyond China, CNOOC said it continued to increase reserves through advanced deepwater exploration in Guyana and signed its first oil contract for exploration in Kazakhstan.

Revenue from oil and gas sales in the first half of 2025 was 171.7 billion yuan, down 7% from the same period last year.

CNOOC's Hong Kong-listed shares closed down 1.84% at HK$18.64 on Wednesday and are down 2.5% so far this year, while the Hang Seng Index .HSI has risen 25.6%.

(Reporting by Sam Li in Beijing and Chen Aizhu in Singapore; editing by Barbara Lewis)

((Sam.Li@thomsonreuters.com;))