CNOOC Ltd, China's biggest offshore oil and gas explorer, posted a 56 percent decline in profit for the first six months of this year.

Net income dropped to 14.73 billion yuan ($2.3 billion), or 0.33 yuan a share, from 33.59 billion yuan, or 0.75 yuan, a year earlier, the Beijing-based explorer said in a statement to the Hong Kong stock exchange on Wednesday. That exceeded the 13.9 billion yuan average of three analyst estimates compiled by Bloomberg.

CNOOC, which depends purely on oil exploration and production for revenue, is most exposed to the oil's plunge this year and must rely on cost cuts and capital spending curbs to boost profit, said Laban Yu, a Hong Kong-based analyst at Jefferies Group LLC.

The strategy paid off last year, when it posted a surprise 6.6 percent profit increase. Brent crude has averaged about $59 a barrel in the first half of the year, down 45 percent from the same period in 2014. The benchmark for half of the world's oil this month slipped below $45 for the first time since 2009.

"There isn't much CNOOC can do to improve earnings prospects in the second half if crude prices fail to rebound," Yu said before the earnings was released.

Net production for the period rose 14 percent to 240 million barrels of oil equivalent.

"The development of the company in the future will be driven by both production and economic efficiency instead of only by production volume," Chairman Yang Hua said in the statement. "We will emphasize economic production volume rather than focus solely on production growth."

CNOOC's oil and gas sales fell to 77 billion yuan in the first six months from 117 billion yuan a year ago.