SINGAPORE, Sept 21 (Reuters) - Light sweet crude in Asia was supported on Friday by firm refining margins, but Vietnam's Bach Ho offer may raise supply and weigh on sentiment for heavier grades. * BACH HO - PV Oil has offered November Bach Ho crude in a tender after a month's halt and indicated that its quality will be heavier than before, trade sources said. Buyers can put in bids for cargoes between 200,000 and 600,000 barrels to be loaded in November. The crude's API gravity could vary from 35.4 to 36.5 degrees, down from the usual 40 degrees. The tender will close on Sept. 25 with bids valid until two days later. * TENDERS - Russia's Sakhalin Energy sold 730,000 barrels of light sweet Vityaz crude for November loading via a tender at the highest premium in four months as firm refining margins buoyed demand, traders said. The cargo for Nov. 19-26 loading was sold at about $5.50 a barrel above Dubai quotes, at a premium around $1 higher than the previous month, they said. Another two cargoes were sold at similar premiums after the tender was awarded. End users in Japan, South Korea and China bought a cargo each. - PV Oil sold the Song Doc cargo to an oil major, likely Shell, at a premium between $6 and $6.50 a barrel to dated Brent, traders said. The cargo will load on Oct. 28-Nov. 2. - India's IOC bought 1 million barrels each of Qua Iboe and EA from Total for November loading. - India's HPCL issued a tender seeking sweet crude for November loading. Part one on grade offers will close on Sept. 24 with prices due on Sept. 25. Offers will stay valid until Sept. 26. * MARKET NEWS - Two more cargoes of North Sea Forties crude oil loading in October have been delayed due to lower-than-expected production, disrupting shipments of the oil that sets the price of the global Brent benchmark. CRUDE Price Prev Change NOV Brent 110.48 107.61 +2.87 NOV Brent/Dubai EFS DUB-EFS-1M 3.60 3.43 +0.17 PRODUCT CRACKS OCT fuel oil crack -4.94 -4.84 -0.10 OCT gasoil crack 19.44 20.04 -0.60 NOV naphtha crack -8.12 -8.22 +0.10 COMPLEX REFINERY MARGINS Today 9.31 Last 5 days 8.44 Last 365 days 7.36

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