A company spokesperson said Sugimori had resigned for personal reasons but declined to give further details. She said Sugimori was also stepping down as the president of the Petroleum Association of Japan (PAJ).

Japan's biggest oil refiner said net profit more than doubled to 221.4 billion yen ($1.7 billion) for the April-June first quarter from 97.6 billion yen a year earlier as stronger oil prices caused a hefty appraisal gain on its inventories, higher refining margins and healthy profits in its energy upstream assets.

Though its net profit exceeded its annual forecast of 170 billion yen, Eneos stuck to its May forecast, claiming uncertainty over prices of energy and metals going forward.

"We didn't revise our full-year estimate as there is uncertainty over prices of oil and copper, which have been weakening recently," Soichiro Tanaka, senior vice president, told a news conference.

"For now, we expect only limited impact on fuel demand from a slowdown of economy," he added.

Eneos is also a major miner and smelter of copper, with copper output from its Caserones mine in Chile rising to 34,000 tonnes in the first quarter from 27,000 tonnes a year earlier.

($1 = 133.0700 yen)

(Reporting by Yuka Obayashi; Editing by Raju Gopalakrishnan)