Global oil markets eased modestly Tuesday, following the biggest single-day surge in more than three decades, but prices could continue to climb in the coming weeks as investors assess the impact of weekend drone attacks on Saudi oilfields and look to U.S. shale production to fill the expected gap in world crude supplies. 

With investors still waiting for a formal assessment from Saudi Arabia as to when it will return its two main oilfields to full capacity following Saturday's attacks, market attention is now turning towards the ongoing boom in U.S. shale production, which the Energy Department expects to reach 8.8 million barrels per day next month. Saudi Arabia's new Energy Minister, Prince Abdulaziz bin Salman, is expected to update the media on the scale of the outages later today.

Around half of that total -- a record high 4.485 million barrels -- is expected to come from the shale-rich Permian Basin that laps between Texas and New Mexico, with increases also forecast for the Bakken region shared by North Dakota and Montana and the Eagle Ford field in north Texas. 

Overall U.S. oil production, which is forecast to reach 13 million barrels per day next year, is expected to be crucial in offsetting the market impact of Saturday's drone attacks on the Abqaiq and Khurais facilities in Saudi Arabia, which have knocked out more than half of the Kingdom's production capacity of 5.7 million barrels per day, a figure that represents around 5% of global supply. 

"Saudi Arabia said that it will use existing inventories to fill the supply gap; however, inventories have already been depleted this year due to output cuts and the supply gap could be overwhelming if the current output disruptions are prolonged," said ING's Warren Patterson.

Brent crude contracts for November delivery, which soared 14.6% yesterday -- the most in more than three decades -- fell $1.08 lower to $ $67.94 per barrel in early European trading, but were still marked at a four-month high.

WTI contracts for October, which are more tightly linked with U.S. gasoline prices, pared some of yesterday's 14.7% advance, the most since December 2008, and were marked 94 cents lower at $61.96 per barrel.

OPEC production cuts, which have taking more than 1.2 million barrels per day from the market since late 2017, and are expected to continue into the first quarter of next year, have not only depleted Saudi Arabia's overall stockpiles but also reduced the so-called supply cushion in global crude markets, making them increasingly vulnerable to disruption-lead price surges.

U.S. sanctions on the sale of crude from Iran, whose exports have fallen more by more than 2 million barrels per day since April, as well as similar restrictions on exports from Venezuela, have kept global markets tight for much of the first half of the year.