LONDON, June 11 (Reuters) -North Sea Troll crude differentials dropped on Tuesday because of a lower offer in afternoon trading while Forties differentials rose slightly after a deal.

BUZZARD FIELD

* The Buzzard oilfield, one of the larger contributors to the Forties crude stream, is still offline while maintenance work is carried out, said a spokesperson for operator CNOOC.

* Reuters reported on May 28 that the field was experiencing a temporary outage.

PLATTS WINDOW

* Indications are on a free-on-board (FOB) basis unless marked as cost, insurance and freight (CIF) or delivered at place (DAP).

* Forties: Vitol bought from Shell CIF Rotterdam July 1-5 at dated Brent plus 75 cents.

* Forties: Glencore offered June 21-23 at dated Brent minus 90 cents.

* The two indications resulted in an FOB average of dated minus 79 cents, according to Reuters calculations, up from the last assessment.

* Troll: Petroineos offered a June 23-27 cargo at dated Brent plus $2.10 CIF Rotterdam.

* Taking into account the Platts quality premium for June Troll cargoes and the freight netback value from CIF Rotterdam to FOB North Sea, the offer equated to about dated minus 54 cents, according to Reuters calculations.

* Johan Sverdrup: BP bid for July 4-13 at dated Brent plus $1.85, up from a bid on Monday.

Reporting by Alex Lawler
Additional reporting by Robert Harvey
Editing by David Goodman

 NORTH SEA CRUDE OIL DIFFERENTIALS AND OUTRIGHT PRICES: 0#BFO-DIF 0#C-E Dated BFO BFO- Brent BFO-BRT BFO-E Forties BFO-FOT FOT-E Oseberg BFO-OSE OSE-E Ekofisk BFO-EKO EKO-E Monthly North Sea crude loading programmes O/LOAD OPEC OPEC NSEA North Sea CRU crude oil PROD oil products DRV derivatives PRO/E European products OILOIL NYMOIL, IPEOIL, OILSPD, OILARB CRDWLDPRODEUR, PRODUS, APROD ENERGY energy speed guide CRUDE/1 crude speed guide