MOSCOW, May 25 (AFP) - Tyumen Oil, the sixth-biggest Russian oil producer, has secured a loan of 197.6 million dollars from the United States' Eximbank to upgrade its Ryazan oil refinery, the company's chief executive said on Tuesday. Tyumen's US-educated boss, Simon Kukes, said the funds were part of a loan package of 500 million dollars (472 million euros) the company was negotiating, the second tranche of which would be used to redevelop its waterlogged Samotlor oil field in Siberia. The oil field, which holds six percent of Russia's known reserves, accounts for more than 85 percent of Tyumen's (TNK) oil production. TNK hopes for a decision on the second loan before the end of next month. "This is very important for us," Kukes said of the Samotlor loan. "It's also important to have it done by June 30 because after June 30, the way it's structured it will be more expensive for us. "Samotlor is by far the most important credit we can obtain ... I hope it will sail through," he told AFP. Overall the loan deals would represent the largest foreign credit to any Russian company since the ruble devaluation and domestic debt default last summer which plunged the economy into deep recession, Kukes said. "After the August crisis it became difficult for Russian enterprises to obtain credits from western financial institutions," he said. "A company must have credibility with western creditors that it will fulfill financial obligations and be able to prove the effectiveness of the project to be financed," he added. Analysts see the loan as a vote of confidence in Kukes' stewardship of TNK, who would only comment: "I am sure the bank took into account the steps which our company has taken ... it's also a kind of reward for the company taking some of the right steps." The Ryazan refinery revamp is part of a TNK strategy to boost its presence in the retail gasoline (petrol) market, the company aiming to produce cleaner fuel and almost double the number of gas stations selling its products from 540 to 1000, also grabbing a 20-percent share of Moscow's retail gas market. Since taking the helm two years ago Kukes has aggressively positioned TNK as a western-style oil giant, adopting a tgwo-pronged approach of increasing capitalisation (market value) and making TNK put the customer at the centre of its business. The result has been a drastic turnaround in profitability with production costs slashed from 12.5 dollars to 3.5 dollars a barrel, and refining costs down from 3.2 dollars a barrel to 85 cents, in part thanks to the ruble's collapse. At the same time the firm has shed 22 percent of its workforce as it struggled to keep its head above water in the facing of collapsing global oil prices, which dipped below 11 dollars a barrel in early March. But with oil producers agreeing to export cutbacks in March prices have recovered, Brent crude for June delivery trading in London last week at a shade under 15 dollars a barrel. That is good news for oil majors such as Tyumen which, although their exports will be cut in the next quarter by 80,000 tonnes -- at a monthly cost of 500,000 dollars according to Kukes -- will see profit margins recover. In March, Kukes told AFP that the company had incorporated an average price per barrel of 10.5 dollars in its business plan, saying a price of 13.5 dollars would boost Tyumen revenues by 150 million a year.  