LONDON, Oct 1 (Reuters) -North Sea Ekofisk crude differentials weakened on Tuesday after a lower offer, while there were no indications on U.S. WTI Midland and other benchmark grades.

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: Gunvor offered Oct. 11-13 at dated Brent plus $1.55, equal to roughly dated Brent plus 58 cents after allowing for the Platts quality premium according to Reuters calculations.

* This is slightly less than Forties and Brent, which were last valued at dated Brent plus 65 cents and for which there were no indications on Tuesday.

* WTI Midland: No indications, last traded last week 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 Shreya Biswas

- 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