Activists in four U.S. states broke into remote flow stations to manually turn off valves on TransCanada Corp's (>> TransCanada Corporation) Keystone line, Enbridge Inc's (>> Enbridge Inc) Line 4 and 67, the Spectra Energy Partners LP (>> Spectra Energy Partners, LP) Express line and a feeder line on Kinder Morgan Inc's (>> Kinder Morgan Inc) Trans Mountain system.

The lines affected were shut down as a precaution, but the disruption was short-lived. By Tuesday afternoon all four companies had restarted the pipelines, helping minimize the impact on prices.

A short-term pipeline shutdown will have little impact on deliveries, shippers in Calgary said. However, longer outages can lead to crude getting bottlenecked in the Alberta marketing hubs of Edmonton and Hardisty, and weigh on prices.

Wester Canada Select heavy blend crude for November delivery last traded at $13.60 per barrel below the West Texas Intermediate benchmark, compared with a settlement price of $13.70 per barrel below WTI on Tuesday.

Light synthetic crude from the oil sands for November delivery last traded at 30 cents per barrel below WTI, having changed hands at 15 cents per barrel under the benchmark on Tuesday.

(Editing by Lisa Shumaker)

By Nia Williams