NEW YORK, July 16 (Reuters) - U.S. cash crude grade differentials gained for the fourth consecutive trading day on Monday despite the tighter arb as U.S. crude prices outpaced expiring North Sea Brent August futures. Mars sour changed hands at $13.70 a barrel, up 85 cents from Friday's high trade of $12.85 above West Texas Intermediate . Light Louisiana Sweet traded as high as $18.10 a barrel, up from Friday's high of $16.65. West Texas Intermediate at Midland added 25 cents to trade at 85 cents under WTI while West Texas Sour traded at $3.50 under WTI, up 35 cents from Friday. The trans-Atlantic crude spread settled at $15.12 on Monday compared with $16.04 in favor of Brent during Friday's trading. U.S. crude futures outperformed Brent on a weaker dollar and hopes for economic stimulus, especially in China. . August Brent oil futures went off the board at $103.55, up $1.15. September Brent settled at $103.37 a barrel, up $1.95. U.S. crude settled up $1.33 to $88.43 per barrel.