The 45-day turnaround at the 190,000 barrel per day Horizon plant in northern Alberta started in mid-September and was meant to be completed by the end of October.

But two market players in Calgary said rumors maintenance may be extended was pushing prices for synthetic barrels delivered in November higher.

A spokeswoman at Canadian Natural was not immediately able to provide an update on the turnaround.

Light synthetic crude from the oil sands for November delivery last traded at $3.10 per barrel over the West Texas Intermediate benchmark, according to Shorcan Energy brokers. On Friday synthetic crude settled at $2.05 per barrel over WTI.

A fire broke out at Horizon on the first day of the turnaround, and at the time Canadian Natural said it was too early to tell if the turnaround would be affected.

Western Canada Select heavy blend crude for November delivery traded at $11.20 per barrel below WTI, tightening slightly from Friday's settle of $11.30 per barrel under the benchmark.

(Reporting by Nia Williams; editing by Diane Craft)

By Nia Williams