* Nov WCS trades at $30.60/bbl below WTI
* Nov synthetic trades at $9.90/bbl below WTI
CALGARY, Alberta, Oct 9 (Reuters) - Canadian heavy crude prices strengthened slightly on Wednesday, although gains were marginal as supply from the oil sands continued to outpace refinery demand.
Western Canada Select heavy blend for November delivery last traded at $30.60 per barrel below the West Texas Intermediate benchmark, according to Shorcan Energy brokers.
That compares with a settlement price of $32.25 per barrel on Tuesday.
Canadian crude prices traditionally weaken during the refinery maintenance season in the autumn and increasing volumes from Imperial Oil's Kearl mining project in northern Alberta have been adding to pressure on prices.
Cenovus Energy Inc is also ramping up production at its 110,000 bpd Foster Creek oil sands project following scheduled maintenance that began in late September.
Meanwhile, repairs at BP Plc's 405,000 barrel per day Whiting, Indiana, refinery, are slowing down a $4-billion revamp that will enable the refinery to run more heavy Canadian crude.
Traders in Calgary said although there was limited scope for big near-term gains, differentials were likely to narrow in the coming quarter as refinery demand improved.
"People are trying to get through this. As soon as Whiting gets going they will start clearing the market," one crude trader said.
Light synthetic crude from the oil sands for November delivery last traded at $9.90 per barrel below WTI, compared with a settlement price of $10.90 per barrel below the benchmark on Tuesday.
Synthetic grades have recovered slightly after trading around $12.60 per barrel below WTI earlier this week, the widest differential since the first quarter of 2012.
Rising production from Syncrude's oil sands project in northern Alberta has pushed synthetic prices sharply lower since the summer. Market sources said some buyers thought the selloff was overdone, even though supply is expected to remain strong.