SINGAPORE, July 27 (Reuters) - Asian jet fuel's premium to gas oil strengthened to a 2-1/2-mth high on Wednesday, as a weakening diesel market continued to widen the spread. The prompt August regrade rose 15 cents to $1.75 a barrel by 0830 GMT, with at least 150,000 barrels transacted at the same level, Reuters data showed. Diesel cracks fell for a fifth session to a shade above $18 a barrel, its lowest level in a month, while the product's August/September contango held at a 7-week low of 45 cents a barrel. Lacklustre regional demand has weighed on gas oil's sentiment, although heavy buying of spot cargoes by traders Glencore and Hin Leong have helped mitigate this. The two parties have accumulated over 7 million barrels of diesel in the pricing window since the start of July, although they did not conclude any trades on Wednesday, Reuters data showed. "The jet market is gaining ground because of gas oil, and that's prompted some buying in the regrade," said a Singapore-based distillates trader. Gas oil swaps trades were thin compared to the previous session, with Glencore the buyer in all 250,000 barrels transacted during the pricing window, down from 450,000 and 600,000 barrels seen on Tuesday and Monday, respectively. In the physical spot market, only one deal of 150,000 barrels of 0.5 percent sulphur gas oil was concluded at lower price levels, which helped widen the grade's cash discount to 48 cents a barrel, down 5 cents. * SWAPS OUTRIGHTS: Gas oil's August swap was down 40 cents at $130.20, while the September swap shed 42 cents to $130.65 a barrel. - Jet swaps for August was 25 cents lower at $131.95 a barrel, with the August regrade (the difference between jet and diesel prices) higher at $1.75, up 15 cents. * CRACKS: Gas oil's crack for August dipped 8 cents to $18.00 a barrel over Dubai crude, the lowest since June 29. - The August jet fuel crack gained 7 cents to $19.75. * CASH DIFFERENTIALS: The discount for gas oil with 0.5 percent sulphur widened 5 cents to 48 cents, while the premiums for the 0.25 and 0.05 percent sulphur grades were steady at 20 cents and $1.00, respectively. - Jet fuel's cash discount was flat at 58 cents. * PHYSICAL OUTRIGHTS: Benchmark diesel with a maximum sulphur content of 0.5 percent fell 45 cents to $129.75 a barrel, while jet fuel lost 25 cents to $131.40. * CASH DEALS: One gas oil deal. - Unipec bought 150,000 barrels cargoes of 0.5 percent sulphur gas oil for Aug. 21-25 lifting from Totsa at a discount of 50 cents a barrel to Singapore spot quotes. PRODUCT RIC BID ASK MEAN PREV CHG % CHG Jet/Kero JET-SIN 131.20 131.60 131.4 131.6 -0.25 -0.19 0 5 Gas Oil 0.5% GO-SIN 129.55 129.95 129.7 130.2 -0.45 -0.35 5 0 Gas Oil 0.25% GO25-SIN 130.25 130.65 130.4 130.8 -0.40 -0.31 5 5 Gas Oil 0.05% GO005-SIN 131.05 131.45 131.2 131.6 -0.40 -0.30 5 5 Jet/Kero Diff JET-SIN-DIF -0.60 -0.55 -0.58 -0.58 0.00 0.00 GO 0.05 Diff GO005-SIN-DI 0.80 1.20 1.00 1.00 0.00 0.00 F GO 0.25 Diff GO25-SIN-DIF 0.00 0.40 0.20 0.20 0.00 0.00 GO 0.5 Diff GO-SIN-DIF -0.50 -0.45 -0.48 -0.43 -0.05 n.a. GO Swap M1 GOSGSWMc1 130.2 130.6 -0.40 -0.31 0 0 GO Swap M2 GOSGSWMc2 130.6 131.0 -0.42 -0.32 5 7 (Reporting by Francis Kan; editing by James Jukwey)

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