TransCanada has shut part of its Keystone pipeline after 5,000 barrels of oil leaked in Amherst, South Dakota, the company said on Thursday, four days before the state of Nebraska was due to decide on an expansion of the system.



The pipeline from Hardisty, Alberta, to Cushing, Oklahoma, and to Wood River and Patoka in Illinois, has been shut, while the southern leg of the system to the Gulf Coast remains operational, the company said.



TransCanada has not given a reason for the incident, which occurred days before the Nebraska Public Service Commission was due to announce a decision on Keystone XL, a 830,000-barrel expansion through the state.



TransCanada said in a statement it discovered the leak 6 a.m. on Thursday after systems detected a drop in pressure, and that it was working with the authorities as it investigates.



Western Canada Select heavy blend crude for December delivery was trading at $14.50 below the West Texas Intermediate benchmark at late afternoon on Thursday, down slightly from $14.20 the day before