Canadian crude prices stabilized in thin trading on May 6 following a two-day rally as a wildfire in northern Alberta kept nearly one-third of Canadian oil sands production shuttered, with no real clarity on when production would resume.

The massive fire has forced the evacuation of Fort McMurray, Alberta's 88,000 residents, as the town, located in the heart of the oil-producing region of the province, has been overwhelmed by flames.

Oil sands companies have shut in at least 720,000 barrels per day (bbl/d) of crude output, according to Reuters calculations, out of Canada's total oil sands production of 2.2 MMbbl/d, though some operators including Syncrude and Imperial Oil have not disclosed how much production is offline.

Some analysts estimated at least 1 MMbbl/d is offline. Yet, they anticipated production will resume without much difficulty, though most companies had not announced when they expect activity to restart. Suncor Energy Inc., which has taken 350 Mbbl/d of capacity offline, said it expects to make a prompt return to full production, and planning for restart is well advanced.

"Clearly, while the disruptions last, they will be price supportive for Western Canadian crude," Julius Walker, senior analyst at JBC Energy GmbH in Vienna, said, adding that high stock levels in the U.S. and Canada mean it "makes sense for refineries to not yet be too concerned about supplies."

The wildfire also stymied transportation of crude and feedstocks normally delivered via trains, pipelines and roads across the vast oil sands, which hold the world's third-largest crude reserves after Saudi Arabia and Venezuela.

Western Canadian Select (WCS) heavy blend crude for June delivery traded at $11.90/bbl under the West Texas Intermediate benchmark on May 6, according to Shorcan Energy Brokers. It settled at $12/bbl under U.S. crude on May 5.

Concerns about temporary shortages boosted light synthetic crude prices on May 5, as the thinly traded May contract doubled in price. It posted one trade on May 6, with light sweet synthetic trading at a premium of $7 to U.S. crude, same as on May 5.

The wildfire has forced 10 oil sands operators including Suncor and Shell Canada to reduce production because workers have had to flee Fort McMurray, and in some cases evacuate operations as a precaution.

More than 20 oil operations are clustered in a 100-kilometer (60-mile) radius of the city, according to government data. Pipelines have also been affected, raising worries about the delivery of diluent, which is normally blended with the viscous bitumen found in the oil sands to produce Canadian heavy crude.