The conflict in Syria has driven a wedge between U.S. and European oil prices, as investors focus on the cushion that booming U.S. production provides against potential supply shocks elsewhere in the world.

U.S. oil futures now are roughly $3.50 a barrel cheaper than Brent, the European benchmark that many experts consider to be a gauge of world prices.

The two contracts were trading in line with each other in July, before tensions in Syria sparked a broad price rally amid fears that U.S. military intervention would disrupt the flow of oil out of the Mideast, which accounts for a third of world oil production.

Workers on a drilling rig in North Dakota, which has been experiencing an oil boom in recent years. Getty Images

But the rise in oil prices on the $207 billion New York Mercantile Exchange futures market was more subdued than the jump in Brent, which investors and analysts attribute to burgeoning U.S. crude output. At the height of the recent tensions, Brent was trading $8 a barrel above the Nymex contract, also known as West Texas Intermediate, or WTI.

The emergence of the gap between Nymex and Brent has reinvigorated more exotic oil-markets bets, in which money managers aim to profit by correctly predicting whether the "spread" will narrow or widen over a certain period.

The two contracts traded within about $1 of each other until 2011, when U.S. oil output began to rise so rapidly that it overwhelmed available pipeline capacity.

That extra oil accumulated in oil tanks across the Midwest, where much of it sat unused, depressing the price.

In October 2011, WTI oil traded at a record discount to Brent of $28 a barrel. Since then, many new pipeline routes have been added, relieving the glut in storage.

Some analysts and investors say those pipelines aren't enough. Earlier this month, U.S. oil output hit 7.75 million barrels a day, the highest level in 24 years.

"There's a disparity that's going to remain between Brent and WTI because there's still not the infrastructure in place to be able to efficiently move that much crude around," said Matt Smith, an analyst at Schneider Electric SA, a consulting firm that helps companies hedge energy-price risks.

To be sure, a resolution to the problems in Syria could close the gap again by easing fears of supply disruptions in the Middle East, analysts say. The price difference between Nymex and Brent has declined in the past week, after Syria said it was open to handing over its chemical weapons.

Meanwhile, thousands of miles away in the heart of the U.S., companies are working to find new ways to get oil to refiners, which can export processed fuel to international markets. John Brynjolfsson, head of investment manager Armored Wolf LLC, pointed to Seaway, a key pipeline that connects Midwest oil producers to Gulf Coast refiners. The companies operating Seaway plan to double capacity from the current 400,000 barrels a day by the first quarter of 2014.

"With Seaway, you're going to have a situation where you have things normalize," said Mr. Brynjolfsson, whose fund oversees about $1 billion. He said he had traded the spread between the two crudes in the past, but didn't place bets on the recent moves.

On Monday, Nymex futures fell 1.5%, or $1.62, to $106.59 a barrel. Brent futures declined 1.5% to $110.07 a barrel.

Still, many investors have their eye on Syria, in case the situation flares up again.

"If Syria escalates, it could cause the spread to widen dramatically," says Emil van Essen, head of commodities trading firm Emil van Essen LLC, which oversees about $260 million. Mr. van Essen in past weeks has been "in and out" of bets that the gap between U.S. and international oil prices will widen.

Investors trading the spread have been closely watching the level of oil stockpiles in Cushing, Okla., the biggest oil-storage hub in the U.S. and the physical delivery point for Nymex oil futures.

The level of inventories at Cushing has fallen for 10 weeks in a row as new pipelines have siphoned off the glut from the Midwest.

But in recent weeks, the rate of the decline has abated, and some investors believe stockpiles, which rose 10% from January to May, could start climbing again, a situation that would likely weigh on Nymex oil prices. In the week ended Sept. 6, supplies fell by 639,000 barrels. In each of the previous nine weeks, stockpiles fell by an average 1.7 million barrels.

Write to Brett Philbin at