The Canadian heavy oil differential widened against the West Texas Intermediate (WTI) benchmark on Friday, as a section of the Keystone pipeline remained closed because of an oil leak in Missouri:* Western Canada Select (WCS) heavy blend crude for March delivery in Hardisty, Alberta, was trading at $11 a barrel below WTI crude futures wider than Thursday's settle at $10.25 below WTI, according to Net Energy Exchange. * A portion of TransCanada Corp's Keystone oil pipeline between Steele City, Nebraska and Patoka, Illinois remained shut on Friday, and there is no estimated return to service, the company said. * Another factor in widening differentials is the Alberta provincial government's easing this month of its forced production cuts, along with decreased rail shipments, a Calgary industry source said. * Light synthetic crude from the oil sands for March delivery traded on par with WTI, compared with Thursday's settle of 15 cents over WTI. * Oil futures edged higher on Friday but ended the week with a loss on renewed concerns about slowing global demand and after the dollar posted its best week in six months.