LONDON, Sept 16 (Reuters) -North Sea Forties and Ekofisk crude differentials rose on Monday after stronger bids, as did those for U.S. WTI Midland which reappeared after a few days' absence from the trading window.

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.

* Forties: Mitsui bid for Oct. 4-13 at dated Brent plus $1.50 and BP offered Oct. 16-18 at dated Brent plus $1.15. The average value of $1.33 is up from Friday's value of dated Brent plus $1.20.

* Ekofisk: Shell offered Oct. 2-4 at dated Brent plus $2.45, the same as an offer on Friday, and Gunvor bid Sept. 28-30 at dated plus $2.65. That boosted the value of Ekofisk to dated plus $2.55 on average.

* Ekofisk: Allowing for the Platts quality premiums for October and September, the indications work out as equal to dated Brent plus $1.42 for dated Brent purposes, according to Reuters calculations.

* WTI Midland: Petroineos bid Oct. 4-8 at dated Brent plus $2.50 CIF Rotterdam, or around dated plus $1.43 on a FOB basis according to Reuters calculations.

* Forties, therefore, stays as the cheapest grade underpinning the benchmark.

Reporting by Alex Lawler, Editing by Tomasz Janowski

 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