U.S. Cash Crude-Grades rise on widened Brent/WTI arb

March 12 (Reuters) - U.S. cash crude differentials rose for the second day on Thursday after the premium for Brent over U.S. crude futures widened.

While U.S. Gulf Coast grades, such as Light Louisiana Sweet and Mars Sour, have in recent months traded in lockstep with the Brent/WTI arbitrage, sources indicated that sour grades seemed to have strengthened separately on higher demand.

Brent's premium over the West Texas Intermediate benchmark (CL-LCO1=R) jumped to $10.03 from $9.37 on Wednesday.

Meanwhile, the United Steelworkers union and oil companies reached a tentative deal to end the largest U.S. refinery strike in 35 years, sources familiar with the new labor accord said Thursday..

Earlier in the day, information provider Genscape said in its mid-week data that Cushing stocks rose some 2.2 million barrels in the four days between Friday through Tuesday, pressuring the futures market quickly on growing stockpiles at the U.S. storage hub

The Houston Ship Channel reopened Thursday morning after a collision earlier in the week. On Thursday afternoon, it was shut again after fog remained in the Houston area.

In the cash market, Light Louisiana Sweet (WTC-LLS) for April delivery into St. James, Louisiana, rose 65 cents and traded between $6.00 and $6.50 a barrel over the front-month light-crude contract.

Mars Sour (WTC-MRS (LSE: MRS.L - news) ) for delivery into Clovelly, Louisiana, rose nearly $1.15 and traded between $3.65 and $4.00 a barrel over the U.S. crude benchmark.

West Texas Intermediate (WTC-WTM) for April delivery into Midland, Texas, rose 20 cents and traded at 75 cents a barrel under WTI.

West Texas Sour (WTC-WTS) rose 40 cents and traded at 60 cents in a regrade over WTI at Midland (WTC-WTM).

In the futures market, U.S. crude fell $1.12 to settle at $47.05 a barrel while international Brent slipped 46 cents to settle at $57.08 a barrel. (Reporting By Catherine Ngai; Editing by Diane Craft)