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

March 12 (Reuters) - U.S. cash crude differentials rose forthe 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 Sweetand Mars Sour, have in recent months traded in lockstep with theBrent/WTI arbitrage, sources indicated that sour grades seemedto have strengthened separately on higher demand.

Brent's premium over the West Texas Intermediate benchmark jumped to $10.03 from $9.37 on Wednesday.

Meanwhile, the United Steelworkers union and oil companiesreached a tentative deal to end the largest U.S. refinery strikein 35 years, sources familiar with the new labor accord saidThursday..

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

The Houston Ship Channel reopened Thursday morning after acollision earlier in the week. On Thursday afternoon, it wasshut again after fog remained in the Houston area.

In the cash market, Light Louisiana Sweet forApril delivery into St. James, Louisiana, rose 65 cents andtraded between $6.00 and $6.50 a barrel over the front-monthlight-crude contract.

Mars Sour for delivery into Clovelly, Louisiana,rose nearly $1.15 and traded between $3.65 and $4.00 a barrelover the U.S. crude benchmark.

West Texas Intermediate for April delivery intoMidland, Texas, rose 20 cents and traded at 75 cents a barrelunder WTI.

West Texas Sour rose 40 cents and traded at 60cents in a regrade over WTI at Midland .

In the futures market, U.S. crude fell $1.12 tosettle 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)