In the energy industry, oil spills are more common than one might think. Though media attention tends to focus primarily on the most devastating ones, smaller ones do happen from time to time, despite the industry's renewed focus on safety measures since the infamous BP (BP -1.17%) Deepwater Horizon incident – the worst accidental oil spill in history.

Just ask ExxonMobil (XOM -0.09%).

ExxonMobil pipeline ruptures
On March 29, ExxonMobil's 940-mile Pegasus crude oil pipeline ruptured near Mayflower, Ark. – a town some 25 miles northwest of Little Rock. According to the Mayflower Incident Unified Command Joint Information Center, the spill has been classified as a major one by the U.S. Environmental Protection Agency. 

The pipeline, which starts in Patoka, Ill., transports some 95,000 barrels per day of mainly heavy Canadian crude oil to a terminal in Nederland, Texas, that is operated by Sunoco Logistics, now part of Energy Transfer Partners (ETP). Exxon reversed the line's flow in 2006 in order to transport crude to the Gulf Coast refining hub.  

Pegasus, which is 20 inches in diameter, serves refineries in the Port Arthur and Beaumont regions. According to Bloomberg, there are four major plants near Nederland – operated by Exxon, Valero (VLO -2.86%), Total, and Motiva Enterprises – that are capable of processing some 1.4 million barrels of crude a day.

At the time it ruptured, the line was transporting Wabasca Heavy Crude from western Canada. Wabasca Heavy is a blend of heavy crude oil produced in Alberta's oil sands by Cenovus Energy, Canadian Natural Resources (CNQ -0.51%), and Suncor Energy. Due to its physical qualities, it is in high demand by U.S. Gulf Coast refiners.

Effect on benchmark crude prices
The line's temporary closure, which will reduce the supply of crude from western Canada and the U.S. Midwest, is likely to worsen the glut of oil in those regions. Due to limited transportation options, crude oil in those two regions has been trading at a substantial discount to the global crude oil benchmark, Brent.

In fact, Western Canada Select (WCS) – the benchmark for western Canadian crude – had been trading at a discount more than $30 even to West Texas Intermediate (WTI) – the primarily U.S. crude oil benchmark – until very recently, due to severe limitations in outbound pipeline capacity from Alberta.

WTI's discount to Brent, which narrowed to its lowest level since July on March 28, increased to $14.01 on Monday, as WTI fell $1.22. Meanwhile, WCS slipped by $0.65 a barrel on Monday and was trading at a roughly $15 discount to WTI toward the end of the day.  

Exxon's response
Exxon is currently under way with an excavation and removal plan for the damaged portion of the pipeline. In an announcement yesterday, the company said it gathered roughly 12,000 barrels of oil and water from the spill.  

It also reportedly deployed fifteen vacuum trucks and 33 storage tanks to the area where the spill occurred. According to a statement by the Unified Command Joint Information Center, Exxon dispatched 120 workers to clean up the mess, who were still steam-cleaning oil from the spill as of yesterday.