SINGAPORE, Sept 21 (Reuters) - Vietnam's state oil marketer 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 on Friday. The offer will increase supply of heavier grades of low sulphur crude in Asia that could weigh on market sentiment. 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. The Vietnamese flagship grade has been absent in the spot market for the past two years as its output was diverted to a local refinery. Exports occurred only when the refinery was shut. But traders expect Vietnam to resume Bach Ho exports on a regular basis as the change in the crude's quality has made the it unsuitable for the refinery. In exchange, PV Oil bought 600,000 barrels of Champion crude to be delivered in October-November. PV Oil last sold Bach Ho for September loading at premiums between $2.50 and $3 a barrel to dated Brent.

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