* July WCS last at $14.80/bbl under WTI
* July synthetic last at $4.25/bbl above WTI
CALGARY, Alberta, June 6 (Reuters) - Canadian cash crude prices strengthened on Thursday as reports that refinery maintenance neared completion spurred expectations for an increase in demand.
Western Canada Select heavy blend for July delivery last traded at $14.80 per barrel below the West Texas Intermediate benchmark, according to Shorcan Energy Brokers.
That compares with a settlement price of $16.00 below the benchmark on Wednesday.
Light synthetic crude from the oil sands for July last traded at a premium of $4.25 per barrel to WTI, up from a settlement price on Wednesday of $2.00 per barrel above the benchmark. Trading sources said the sharp rise was difficult to explain.
Heavy oil prices have been rising in recent days on reports that two major refineries that process Canadian crude could return to service this month after prolonged shutdowns.
Oil market intelligence service Genscape said Exxon Mobil Corp's 238,600 barrel per day refinery in Joliet, Illinois, was conducting preliminary restart activities.
The facility, which processes Canadian crude, shut down for maintenance on April 14 and is likely to return to service before the end of this month, according to Genscape.
Meanwhile, BP Plc said an upgraded crude distillation unit at its 405,000 bpd Whiting, Indiana, refinery is on schedule to start up by the end of June.
Prices showed little reaction to news that Phillips 66 is conducting planned maintenance at its 362,000 bpd joint-venture refinery in Wood River, Illinois.
The company did not give details regarding specific units involved or the duration of the work, but market sources said the maintenance work had already been factored into prices.