Oct. 21 (Bloomberg) -- Premiums for U.S. Gulf Coast crude oils weakened as West Texas Intermediate’s discount to Brent narrowed for the fourth time this week.

The gap between WTI and Brent December contracts narrowed $1.53 to $22.16 at settlement. The spread for prompt month contracts settled at a record $27.88 a barrel Oct. 14.

When Brent decreases versus WTI, it weakens the value of low-sulfur U.S. grades that compete with West African oil priced against the European benchmark.

Heavy Louisiana Sweet’s premium to WTI lost $1.20 to $26.80 a barrel as of 3:53 p.m. New York time while Light Louisiana Sweet shrank $1 to $28 above the U.S. benchmark.

Among sour, or high-sulfur, grades, the premium for Mars Blend decreased 70 cents to $21.70 a barrel and Poseidon increased 35 cents to $21.50 a barrel over WTI.

Southern Green Canyon’s premium lost 45 cents to $21 a barrel and West Texas Sour’s discount was unchanged at 70 cents a barrel. Thunder Horse’s premium decreased $1.30 to $23.70 above the benchmark.

The discount for Western Canada Select widened 20 cents a barrel to $10.95 below the price for WTI.

Syncrude’s premium to WTI weakened 25 cents to $12.50 a barrel. Syncrude is a light, low-sulfur synthetic oil derived from the tar sands in Alberta.

--Editors: Charlotte Porter, Richard Stubbe

To contact the reporter on this story: Aaron Clark in New York at aclark27@bloomberg.net

To contact the editor responsible for this story: Dan Stets at dstets@bloomberg.net