(Corrects story published on May 27 to clarify in the second paragraph that Gunvor is handling 30-40 percent of oil exports from firms like Rosneft, not the bulk of exports)

MOSCOW, May 27 - One of Russia's most secretive businessmen, Gennady Timchenko, revealed on Wednesday he has built up an 18 percent stake in gas firm Novatek as he seeks to diversify his oil wealth into other industries.

Timchenko co-founded the world's third-largest crude oil trader by volume, Switzerland-based Gunvor, which has annual revenues estimated at $70 billion and handles 30-40 percent of exports from the likes of state oil major Rosneft .

Gunvor's rapid growth prompted speculation the firm enjoyed special support from the Kremlin, although Gunvor's competitors say the trader often offers healthy premiums to outbid rivals.

Last year, the mysterious tycoon wrote an open letter headlined Gunvor, Putin and me, saying media speculation about his close ties with the former Russian president and current prime minister, Vladimir Putin, were overblown.

On Wednesday, after a year of virtual complete public silence, Timchenko announced through his fund, little known to date Luxembourg-based Volga Resources, that he had increased his stake in Novatek by 13.13 percentage points to a total of 18.2 percent.

Novatek is Russia's second-largest gas producer after state-run giant and gas export monopoly Gazprom , which holds a stake of 19 percent in Novatek -- now only slightly more than Timchenko.

The purchase of 13 percent in Novatek would have cost Timchenko $1.56 billion at today's market price. Volga Resources said it bought the shares from Novatek's management.

Novatek traded at $45.2 per GDR in London at 1320 GMT (9:20 a.m. EDT), up from as low as $13 in December but down from $97 last May, when Russian markets reached their peaks.

CONFUSION OVER PAYMENT

Shares in Novatek rose 7 percent in Moscow, outperforming the broader market <.MCX> as traders said news about Timchenko and Tuesday's announcement that Novatek bought new gas reserves supported the stock.

Both Gazprom and Timchenko are very close to the country's leadership and most likely their big political influence will help Novatek solve whatever problems it has, said Valery Nesterov from Troika Dialog brokerage.

On Tuesday, Novatek said it would pay $650 million to buy 51 percent in gas firm Yamal LNG, which controls the giant South-Tambeyskoye Arctic natural gas field.

Novatek said the seller of Yamal LNG was Volga Resources but did not name Timchenko.

The fund itself said later that Volga was created in 2007 by Timchenko to invest in oil, gas, infrastructure and development projects in the former Soviet Union, Eastern and Central Europe and Turkey.

South-Tambeyskoye has reserves of up to 1.3 trillion cubic meters -- equal to 45 percent of global annual gas consumption. By comparison, Gazprom controls a fifth of global gas reserves, enough to supply the world with gas for over 10 years.

Business newspaper Kommersant quoted unnamed sources on Wednesday as saying Novatek would grant $650 million worth of its shares to Timchenko in return for his stake in Yamal LNG.

But Novatek said on Wednesday the deal did not involve equity. It is a cash deal ... in several tranches. The first tranche will probably be next week, said Chief Financial Officer Mark Gyetvay, adding that the remaining sum could be raised from the debt market.

UniCredit analysts said in a note the Yamal LNG acquisition appeared cheap but an objective appraisal of the reserves was difficult at the moment.

We cannot be sure of the development costs, which may include construction of the cross-Yamal pipelines and/or an LNG plant above the Arctic circle, UniCredit said.

(Writing by Dmitry Zhdannikov; Editing by David Cowell and Jon Loades-Carter)

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