* March WCS quoted at $24.25/bbl under WTI * Narrowest WCS spread since Oct 23 * March synthetic $1.30/bbl over WTI CALGARY, Alberta, Feb 8 (Reuters) - Canadian heavy crude prices rose on Friday for the sixth straight session this month as reduced pipeline rationing made for improved access to markets and as Imperial Oil Ltd worked to return operations at an Ontario refinery to normal. Western Canada Select heavy blend for March delivery last sold for $24.25 a barrel under benchmark West Texas Intermediate, narrowing its discount from a Thursday settlement of $25 a barrel under, according to Shorcan Energy Brokers. That was its tightest differential since Oct 23. WCS gains have been steady after two months of discounts that at times topped $40 a barrel. Surging production, tight pipeline capacity and a series of refinery outages were blamed for the slump, and those fundamentals are largely unchanged. Imperial said it was returning operations at the 121,000 barrel a day Sarnia, Ontario, refinery to normal following a undisclosed problem at the end of January. Apportionment levels on Enbridge Inc's pipeline network to the U.S. Midwest are below those set for last month, easing some of the price pressure, traders have said. In addition, the start-up of Imperial's 110,000 barrel a day Kearl project in northern Alberta, first expected to begin commercial production at the end of 2012, is now targeted for the end of the first quarter. Full production is scheduled for the "next several months". Light synthetic crude prices also gained on Friday. It was last quoted at $1.30 a barrel above WTI, up 40 cents from Thursday. This week, Suncor Energy Inc and Syncrude Canada reported lower oil sands-derived crude production for January.