Canadian heavy crude rallied to a two-month high relative to U.S. crude this week, offering some relief to oil producers in Alberta struggling with thin margins amid plentiful supply. The rally was likely to be short-lived, traders and analysts said, because output continues to grow without a corresponding increase in transportation capacity. Canada’s crude typically trades at a discount to U.S. benchmark West Texas Intermediate (WTI) light oil, reflecting transportation costs to U.S. refineries and additional processing requirements. The discount expanded since a November leak in TransCanada Corp’s Keystone pipeline, which led to a temporary shutdown and a buildup in supplies. TransCanada is now operating the line at reduced pressure. Canadian producers have been unable to boost volumes by rail much, as railways are reluctant to take more oil business when they are busy shipping grain.