SINGAPORE, Feb 7 (Reuters) - Values of April-lifting Qatar Marine crude are expected to firm over the previous month after a cut in official selling prices (OSP) of the grades boosted buying interest, traders said on Tuesday. April Qatar Marine could change hands at around 20 cents a barrel below Dubai quotes, up from a discount of 70-80 cents last seen for March cargoes. The grade's OSP for January was set on Monday at a premium of $2.40 to Dubai quotes, a greater-than-expected cut of 67 cents from the previous month. Trading of April cargoes of Middle East crude is expected to start next week, traders said. * OSP - Yemen has set the official selling price (OSP) of its Masila crude for loading in April at a premium of $2.55 a barrel to dated Brent, up 40 cents from the previous month, the Yemeni government said late on Monday. Unipec, the trading arm of China's largest refiner Sinopec , was the highest bidder and will load all 2.4 million barrels of Masila crude available in April, the government said in a statement sent by email. Yemen set the April OSP for Marib Light crude at parity to dated Brent, steady from the previous month. The government did not announce quantities for Marib Light crude. * TRADES - SK Energy sold one Dubai partial to Trafigura at $113.30 a barrel. * EFS - Front-month Brent/Dubai Exchange of Futures for Swaps (EFS) for March DUB-EFS-1M rose 7 cents to $2.90 a barrel. * OMAN ASSESSMENTS - April Oman traded on the DME was valued at a premium of $2.15 cents 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 - China's top refineries will trim their crude oil processing in February to the lowest in four months after running hard in winter to meet a seasonal demand spike and ensure ample supplies during Chinese New Year holidays. - Brent crude's premium to U.S. oil could be poised for another record run after jumping 50 percent over the past week, as an expected build in Midwest inventories again exerts pressure on the U.S. benchmark. - Iraq's Majnoon oilfield, operated with Royal Dutch Shell, is expected to reach 175,000 barrels per day (bpd) production by August this year from current output of 54,000 bpd, a senior official at state-run South Oil Company said on Tuesday. * REFINERY MARGINS - The complex refining margin for Dubai in Singapore was $9.32 per barrel, up from an average of the last five days of $9.90, Reuters data show. Over the last year, the average margin has been $8.16 cents per barrel. * CRACK SPREADS - Fuel oil's March crack fell 47 cents to a discount of $3.76 a barrel to Dubai crude. - Gasoil's March crack strengthened 30 cents to a premium of $18.57 a barrel to Dubai crude. - Naphtha's front-month crack firmed 45 cents to a discount of $5.76 a barrel to Brent crude. * OUTRIGHT PRICES - March ICE Brent was at $115.79 a barrel by 0830 GMT, up $1.69 from the previous session. - April Oman was trading at $114.61 by 0830 GMT, up $1.94 from Monday.

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