* Crude futures seesaw, end slightly higher * Brent-U.S. crude spread also choppy, ends narrower NEW YORK, July 15 (Reuters) - Cash crude differentials inthe United States strengthened on Monday, reacting to atrans-Atlantic spread that widened intraday before endingnarrower, traders and brokers said. Brent crude's premium to U.S. crude ended at$2.77 a barrel based on August contract settlements, narrowingthe spread only nine cents after it ended at $2.86 on Friday. But the spread ranged from $2.59 to $3.46 on Monday, not toodissimilar to Friday's range of from $2.41 to $3.36. The spread shrank to $1.32 intraday last Thursday, thenarrowest between front-month contracts since November 2010. The stronger differentials for many trades completed forcash crude grades on Monday reflected the wider spread intraday,traders said. Usually, the wider the arbitrage, the more supportive it isfor U.S. cash crude differentials, while a narrower spread oftenpressures differentials. This especially holds true for sweetgrades, which are priced in line with global waterborne crudessuch as Brent. Crude oil futures edged higher on Monday in thin trade,reversing after slumping early in the session, as tradersdigested mixed economic and industry data from the United Statesand China, the world's biggest oil consumers. The Brent August crude contract expires on Tuesday. CASH CRUDE TRADES Light Louisiana sweet crude oil for August deliverytraded on Monday from $5.35 to $5.70 over the benchmark U.S.August crude futures. That range for differentials was stronger than Friday'strades completed from $4.70 to $5.20 over the benchmark. Mars sour crude, a Gulf of Mexico-produced grade,traded at 82 cents and 85 cents and $1.00 under the futuresbenchmark, stronger after trading Friday from $1.20 to 90 centsunder the benchmark. Eugene Island traded at $2.70 over the futuresbenchmark. That differential was stronger than offers fromsellers seen pegged at $2.50 over the benchmark on Friday. Southern Green Canyon crude traded at $1.45, $1.55and $1.65 under the futures benchmark, stronger after Friday'strading at $2.00 and $1.70 under the benchmark. Bakken crude at the Clearbrook, Minnesota, hub hadbids seen at $4.00 under and offers from sellers at $3.00 underthe futures benchmark, that was weaker than Friday's bid-offerspread pegged at $3.00/$2.50 under the benchmark. Bakken recently was having its differential supported byreduced production from Syncrude Canada Ltd's oil sandsoperations, due to maintenance work at its Alberta project. The cost of moving Bakken to refineries by rail has helpedstrengthen LLS and the differentials of other competing U.S.cash crude grades and thinned spot trading for Bakken, accordingto a Texas-based broker. Bakken differentials might come under pressure in order tocompete with grades closer to refineries, the broker said. MIDLAND GRADES West Texas Intermediate crude at Midland traded at 40and 35 cents under the futures benchmark on Monday after tradingon Friday at 55 and 45 cents under the benchmark. West Texas Sour crude, also at Midland, traded at 25and 20 cents under the futures benchmark after Friday's trade at20 cents under the benchmark. CRUDE FUTURES Brent August crude rose 28 cents, or 0.26 percent,to settle at $109.09 a barrel. The Brent August contract expireson Tuesday. U.S. August crude rose 37 cents, or 0.35 percent, tosettle at $106.32 a barrel. (Reporting by Robert Gibbons. Editing by Andre Grenon)