OPEC spoiler alert sends oil prices lower Monday

 A resilient U.S. shale oil sector and the jitters over a spoiler for the OPEC effort to balance the market sent crude oil prices lower on Monday.

North American crude oil prices are under pressure in part because the Keystone pipeline network remains shut in after a release in North Dakota. Of the major crude oil price benchmarks, Western Canadian Select, the Canadian benchmark for the price of oil, is down the most early Monday as much of the Keystone oil remains locked north of the U.S. border.