Aug 25 (Reuters) - PetroChina Co Ltd(601857.SH) , the world's second-most valuable oil and gas producer after Exxon Mobil Corp , posted a marginal rise in first-half net profit as higher oil prices and strong production offset losses in its refining sector and costly natural gas imports.

PetroChina posted a net profit of 66 billion yuan ($10.3 billion) for the first six months, up 1.03 percent from 65.33 billion yuan a year earlier, in a statement to the Hong Kong Stock Exchange on Thursday.

The profit missed a 68.33 billion yuan estimate from nine analysts polled by Reuters.

PetroChina, China's largest oil producer, and offshore focused peer CNOOC Ltd , have benefited from high crude prices in the first half, which averaged about $110.5 per barrel for Brent crude.

Losses in PetroChina's refining sector curbed gains, as the government held back from increasing domestic fuel prices because of inflation concerns. Expensive natural gas imports have also eaten into company earnings. (Reporting by Wan Xu and Farah Master; Editing by Matt Driskill and Chris Lewis)