* June WCS quoted at $17.50/bbl under WTI
* Unit at Imperial's Sarnia plant down for several weeks
* Light synthetic quoted at $2.25 over WTI
CALGARY, Alberta, May 8 Canadian heavy crude
prices weakened on Tuesday as an unscheduled outage of a unit at
Imperial Oil Ltd's Sarnia, Ontario, refinery led to a
back-up of supplies in the U.S. upper Midwest, market sources
Western Canada Select heavy blend for June delivery last
sold for $17.50 a barrel under benchmark West Texas
Intermediate, a $2.25 deeper discount than on Monday.
Imperial said on Tuesday that a coker unit at its 121,000
bpd Sarnia plant will be down for several weeks of maintenance
following a weekend disruption, and that the shutdown would
allow it to conduct other work at the plant as well.
Other parts of the refinery will remain operating during the
work, the company said.
The outage has prompted players to seek delays to supplies
on the Enbridge pipeline system into Stockbridge,
Michigan, and Sarnia, an oil marketing source said.
"(There is) a bit of a glut forming," the source said.
Imperial said parts of its 112,000 bpd Nanticoke, Ontario,
refinery are also down for several weeks of planned work.
Potentially affecting business on Wednesday, it was reported
that an incident at the 74,000 bpd Sinclair Oil refinery in
Wyoming sent four workers to hospital. Local media said the
incident was at the gas recovery unit.
Impact on the plant's operations was not immediately known.
The refinery gets Canadian crude from Kinder Morgan's
Light synthetic for June also weakened on Tuesday. It last
sold for $2.25 a barrel over WTI, compared with a $2.50 a barrel
premium on Monday.