* February WCS quoted at $39.25/bbl under WTI
* February synthetic quoted at $0.25/bbl under WTI
* Enbridge sets mid-month apportionment on 3 pipelines
CALGARY, Alberta, Jan 10 (Reuters) - Canadian heavy crude prices sank on Thursday after Enbridge Inc imposed mid-month apportionment on three of its pipelines in Canada and the United States, squeezing already-tight export capacity, market sources said.
Western Canada Select heavy blend for February delivery last sold for $39.25 a barrel under benchmark West Texas Intermediate, a $2.15 deeper discount than on Wednesday, according to Shorcan Energy Brokers.
Enbridge imposed new apportionment on Lines 4, 67 and 6A after a series of operational issues across its system threatened to force large volumes scheduled to move this month to be held over into February.
When pipelines set apportionment, they reduce the actual volumes that shippers can move from the amount nominated. Because less crude can move through the pipeline, a backlog occurs.
The 796,000-barrel-per-day Line 4, between Edmonton, Alberta, and Superior, Wisconsin, and 450,000 bpd Line 67, between Hardisty, Alberta, and Superior, are apportioned at 10 percent. Line 6A, which can carry 609,000 bpd between Superior and Griffith, Indiana, is apportioned at 16 percent.
Line 6A had already been apportioned by 10 percent.
Canadian heavies have been under severe pressure for several weeks as some major U.S. refineries underwent maintenance, pipeline capacity remained tight and supplies were set to increase with the start-up of Imperial Oil Ltd's 110,000 barrel-per-day Kearl oil sands project.
Light synthetic for February, meanwhile, last sold for 25 cents a barrel under WTI, down from a day-earlier settlement of 10 cents above WTI.