LONDON, Sept 25 (Reuters) -North Sea Ekofisk and Brent crude differentials weakened on Wednesday while Forties strengthened and U.S. WTI Midland was steady.

PLATTS WINDOW

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

* No deals, a trade source said.

* Ekofisk: Conoco offered Oct. 8-12 at dated Brent plus $1.75, lower than an offer on Tuesday and equal to roughly dated Brent plus 78 cents after allowing for the Platts quality premium according to Reuters calculations.

* Brent: Petroineos offered Oct. 20-22 at dated Brent plus $1.00, below the last assessment.

* Forties: Gunvor bid at dated Brent plus 85 cents and Exxon offered at dated Brent plus $1.20. This resulted in an average of dated plus $1.03, above Tuesday's assessment.

* WTI Midland: No indications, last traded on Monday at dated Brent plus $2.75 CIF Rotterdam or about plus $1.88 on a FOB basis according to Reuters calculations.

* Ekofisk becomes the cheapest grade in the dated Brent basket, and therefore set the benchmark price.

Reporting by Reuters; Editing by Kirsten Donovan

- 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