May 20 (Bloomberg) -- Nippon Mining Holdings Inc., Japan’s largest copper producer and an oil refiner, rose the most in almost two weeks on speculation oil demand will improve and after announcing increased investment in solar energy.

The shares rose as much as 6.8 percent to 562 yen, the biggest gain since May 7, and traded at 560 yen at 10:58 a.m. in Tokyo. It was the third-biggest winner on the Nikkei 225 Stock Average.

Oil traded near $60 a barrel in New York after rising for a second day because of declines in U.S. stockpiles and gains in equities. Nippon Mining said yesterday it would invest 30 billion yen ($313 million) in a solar materials plant to start production next April.

“It’s matter of time before oil and copper prices regain strong upward momentum in tandem with an expected recovery in the global economy,” said Hidetoshi Shioda, a senior energy analyst at Mizuho Securities Co. in Tokyo. “Nippon Mining’s announcement yesterday about boosting investment in solar-power materials production may be a partial reason behind today’s shares surge.”

Nippon Mining will merge with Nippon Oil Corp., Japan’s biggest refiner, in April 2010 to cut costs of 60 billion yen as a slump in fuel demand forces Japanese refiners to reduce output and shut plants. The shares have almost doubled since the announcement on Dec. 4.

“The planned merger with Nippon Oil next year will give a cost-reduction benefit to Nippon Mining and a strong bullish impact on the share price,” Shioda said.

To contact the reporters on this story: Shigeru Sato in Tokyo at ssato10@bloomberg.net.

Last Updated: May 19, 2009 22:08 EDT