Ath is very very heavy on WCS production.
see article below from 430 today
Heavy Western Canadian Select crude in Alberta traded at a $25-a-barrel discount to US benchmark West Texas Intermediate on Tuesday, the widest since January, according to data compiled by Bloomberg. The difference was $10.20 a barrel in early July. A grade of light crude called Edmonton Mixed Sweet hit a discount of $5.65 on Monday, the widest in almost two years.
Canada’s pipelines have been forced to ration their space this year amid signs oil production is rising before the startup of the expanded Trans Mountain pipeline system next year. For November, Enbridge Inc. increased apportionment on its Mainline system, the country’s largest oil export pipeline network, to the most in about two years.
Alberta’s total crude output rose to 3.01 million barrels a day in August, the highest since May, Alberta Energy Regulator data show. But the true output is almost certainly higher as the data has excluded output from Suncor Energy Inc., one of the largest oil-sands producers. The increased production is coming amid a heavier-than-usual refinery maintenance season in the US, which has spurred increased Canadian oil exports off the US Gulf Coast.