SINGAPORE, April 29 (Reuters) - Attention in the Middle East crude market turned to the release of official selling prices from major producers next week as traders sought confirmation of a weakening trend in spot values on the back of a recent fuel oil decline. June spot Oman cargoes were valued at a 70-cent premium to Dubai quotes on Friday, down from about 80 cents a day earlier, traders said, as fuel oil cracks remained near 30-month lows. * SAUDI OSP PREVIEW - Top oil exporter Saudi Arabia may lower the official selling price (OSP) for June Arab Heavy crude in response to lower fuel oil, while leaving values for lighter grades little changed, in an attempt to re-balance sweet and sour supplies. [ID:nL3E7FT0OZ] - Traders polled at five refiners of Saudi crude in northeast Asia said they expected the discount of Arab Heavy to widen, with the forecast decline ranging 10-50 cents to as low as $3.95 a barrel below the average of Oman and Dubai crudes. - Arab Heavy's $3.45 discount for May was already the biggest since February 2009, as ample supplies of Middle East crude relative to limited availability of light sweet grades have forced the kingdom to settle for less. - A tight market for sweet crude may help the Saudis keep prices of Arab Light steady and even boost the value of naphtha-rich Arab Extra Light, the poll showed. - Naphtha cracks are at their highest since March 10, the day before Japan's earthquake, while for fuel oil the crack has dropped to a discount of about $14 a barrel to Dubai crude, near a 30-month low and down about $5 from a month ago. - "The fuel oil crack is weak, but the Dubai structure is still supportive, so it's not easy for them to lower too much," another trader said, referring to the heavier grades. - The premium of front-month Dubai crude swaps over the second month has stabilised slightly above 25 cents a barrel, reflecting Asian refiners' readiness to pay more for prompt barrels of Middle East crude. * OMAN & DUBAI OSPs - The official selling price (OSP) for Oman crude in June will rise by $7.56 to $116.51 a barrel, Reuters calculations based on data from the Dubai Mercantile Exchange (DME) showed. - The June Dubai crude OSP, set 40 cents below DME Oman, was calculated at $116.11 a barrel. [ID:nL3E7FT1B4] * EAST-WEST - The front-month Brent/Dubai Exchange of Futures for Swaps (EFS), an indicator for the premium of light sweet grades over heavy sour supplies, gained 10 cents to $6.51 a barrel, after reaching $7.86 earlier this month, the widest in more than five years, Reuters data showed. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ For a graphic of the EFS and the Dubai forward curve: here ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^> * DME OMAN - June Oman traded on the Dubai Mercantile Exchange (DME) rose 37 cents to a premium of 47 cents a barrel to Dubai swap quotes at 0830 GMT, using the settlement price for DME futures, the ICE one-minute marker for Singapore and the Brent-Dubai EFS as calculated by Reuters. * MARKET NEWS - A tanker with the first major oil shipment from rebel-held east Libya is expected to arrive in China next week, but it remained unclear who the buyer of the cargo is. [ID:nL3E7FT05I] - The Liberia-registered tanker Equator, reported to be carrying 80,000 tonnes of crude, left the rebel-held east Libyan port of Marsa el Hariga three weeks ago, carrying fuel exports vital to financing the uprising against Muammar Gaddafi. - China's state-owned oil companies can cover any shortages of refined fuel products under plans to shut small refiners known as "teapots" that make up 10 to 15 percent of the country's capacity, though fuel oil imports would fall sharply. [ID:nL3E7FS3GW] * CRACK SPREADS - Fuel oil's May crack edged up 39 cents to a discount of $13.95 a barrel to Dubai crude, while the June crack discount gained 43 cents to minus $13.72 a barrel. - Gas oil's May crack was 23 cents higher at a premium of $19.59 to Dubai crude, while June's crack premium strengthened 37 cents to $20.08 a barrel. - Naphtha CFR Japan's June and July cracks both rose 62 cents to a discount of $4.49 and $4.73 a barrel to Brent crude. * OUTRIGHT PRICES - June ICE Brent LCOc1 was at $124.60 a barrel at 0830 GMT, down $1.16 from Thursday. [O/R] (Reporting by Alejandro Barbajosa, editing by Anthony Barker)

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