The Keystone Oil Pipeline was previously shut down after tests showed possible safety issues, but it's up and running again.
The pipeline carries 590,000 barrels of oil across Canada to the Midwest.
Oil began to flow again when Transcanada restarted the pipeline yesterday.
A Transcanada Company Spokesman says the system will be operating with a reduced pressure for 24 hours and normal delivery levels will start back up in November.
The potential problems deducted before were between Missouri and Illinois, but Transcanada says there were no leaks in the pipeline.
