North Sea Crude-BP buys 4th Forties this week

* Forties steady at dated Brent plus 70 cents

* North Sea output to fall by 1 percent in November

* Swaps in backwardation

LONDON, Oct 11 (Reuters) - North Sea Forties crude differentials remained at a strong premium to dated Brent on Thursday, supported by demand from BP, signs of tight supply in November and expectations of stronger refinery demand.

BP purchased its fourth cargo this week on Thursday and rival traders expect the oil to be loaded onto a Very Large Crude Carrier bound for South Korea, removing a chunk of supply from northwest Europe.

Shipments of Forties to South Korea, encouraged by a free trade agreement during 2012, tend to support prices in the North Sea market, as well as Brent swaps and timespreads.

"Forties arbitrage to Asia together with a downtick in offline NWE refining capacity in November and a still relatively tight loading programme does paint a bullish picture," said Eugene Lindell, analyst at JBC Energy in Vienna.

He added, though, that actual November loadings of Forties may be higher if delayed cargoes from October are brought into the first 10 days of November.

FORTIES

* BP bought from a Forties loading Oct. 26-31 at dated plus 70 cents, the same as a trade on Wednesday, and the fourth cargo it has bought in the Platts window this week.

* Also in the window, BP bid for an Oct. 31-Nov. 7 Forties at dated plus 45 cents.

NOVEMBER SUPPLIES

* Supply of the 12 North Sea crudes tracked by Reuters will average 1.95 million barrels per day (bpd) in November, down from 1.97 million bpd in October, according to Reuters calculations on Thursday based on loading programmes.

* Almost the entire Forties programme for October has been deferred due to a slower-than-expected return to production of the Buzzard offshore oilfield, Britain's biggest, after a maintenance shutdown.

SWAPS

* The swaps curve remained in a backwardation, although not so steep at the front end as on Wednesday:

15-19/10 Dec +100 22-26/10 Dec +90 29-02/11 Dec +63 5-9/11 Dec +40 12-16/11 Dec +15 19-23/11 Dec -6 DATABASE

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(Reporting by Alex Lawler; editing by Keiron Henderson)

((alex.lawler@thomsonreuters.com)(+44 207 542 4087)(Reuters Messaging: alex.lawler.reuters.com@reuters.net))

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NORTH SEA CRUDE OIL DIFFERENTIALS AND OUTRIGHT PRICES:

Dated BFO Brent Forties Oseberg Ekofisk Statfjord Flotta

Monthly North Sea crude loading programmes

North Sea Sullom Voe shipments

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Keywords: MARKETS EUROPE CRUDE/