* November synthetic trades at $10.50/bbl below WTI
* November WCS last at $31.90/bbl below WTI
CALGARY, Alberta, Oct 1 (Reuters) - Canadian light synthetic crude prices weakened on Tuesday, the first day of the October trading window, as a result of refinery outages and robust supply.
Light synthetic crude from the oil sands for November delivery last traded at $10.50 per barrel below the West Texas Intermediate benchmark, according to Shorcan Energy brokers.
That compares with a settlement price of $7.00 per barrel below WTI on Monday, and was the lowest level since the first quarter of 2012, according to Reuters data.
Traders in Calgary said healthy supply from Syncrude's northern Alberta oil sands project was weighing on prices.
"There's too much production and not enough pipelines," said one Calgary crude trader, referring to the congested export network which can leave oil bottlenecked in Canada.
Suncor Energy Inc shut down a 32,000 barrel-per-day hydrocracker unit at its 85,000 bpd refinery in Sarnia, Ontario, after a small fire broke out.
BP Plc's joint-venture 135,000 bpd Toledo refinery was reported last week to be running at reduced rates.
Canadian crude prices historically weaken in the fourth quarter of each year as a result of reduced demand in winter.
Western Canada Select heavy blend for November delivery was steady at $31.90 per barrel below WTI, unchanged from Monday's settlement price.
The differentials on Canadian heavy grades have also widened steadily since the summer.
BP's 405,000 bpd Whiting, Indiana, refinery has been undergoing a revamp to enable it to run more heavy Canadian crude, but problems with the construction of a coking unit means the work could continue past the end of 2013.