US Crude Outlook - Diffs may firm on economic recovery

*Futures rise to 18-month high on U.S. economic recovery

*Cash crude may firm on refiner demand, hijacked cargo

NEW YORK, April 5 (Reuters) - U.S. cash crudes may firm this week after positive economic data show the economy in recovery, potentially boosting fuel demand, while a 2-million-barrel oil cargo bound for the U.S. Gulf Coast was hijacked off of East Africa over the weekend.

U.S. oil futures CLc1 rose to an 18-month high on Monday near $87 a barrel after U.S. payrolls increased rapidly in March, the service sector expanded and pending home sales rose.

The spread between May and June U.S. crude futures widened 2 cents to 49 cents a barrel, while WTI's premium to brent expanded to 86 cents a barrel from 81 cents on Thursday, when futures had last traded in New York.

"Most grades should get a tad higher this week," said one cash crude trader. "The domestic heavy sour crudes could get a lift after the tanker seizure, although there is plenty of crude in the market."

Somali pirates seized the 2-million-barrel capacity South Korean Samho Dream very large crude carrier (VLCC) offshore East Africa over the weekend. The ship had been chartered by Valero Corp to transport crude from Iraq's Basra port to the U.S. Gulf Coast. [ID:nLDE633091]

Crude traders and brokers said the tanker seizure could help sour crudes such as Mars MRS- gain in trading, although they did not expect any major buying spree to take place.

"They'll be buying little by little so they don't push the market up," said a source at a U.S. refiner.

Any effect of the tanker seizure appeared minimal early Monday. Mars was talked in a range of $3.90 to $4.10 a barrel below West Texas Intermediate early Monday, versus a range of -$3.80 to -$4.00 on Thursday.

Light Louisiana Sweet LLS- was talked at up to $1.25 a barrel above WTI, in range with Thursday's levels.

Some U.S. refineries may be emerging from spring maintenance soon, boosting demand for crude ahead of the U.S. driving season.

U.S. refinery margins were mixed last week, with Mid-Continent margins making the biggest gain and the Rockies region posting the largest decline, Credit Suisse said in a weekly report Monday.

Midwestern margins rose 54 cents, or 5.9 percent, to $9.80 a barrel last week. In the Gulf Coast, margins rose 29 cents to $8.98 a barrel, while West Coast margins inched up 20 cents to $15.78 a barrel. In the Rockies, margins dropped $1.23, or 7 percent, to $16.47 a barrel.

Tesoro Corp (TSO.N) said on Sunday crude oil intake at its Anacortes, Washington, refinery was down to about 70 percent of its 120,000 barrel per day (bpd) capacity following a deadly explosion and fire on Friday. Production of clean gasoline and diesel at the Anacortes facility was down to one-third of normal, or about 25,000 bpd, according a statement by Tesoro spokesman Lynn Westfall. (Reporting by Joshua Schneyer, editing by Bob Burgdorfer)