May's discount to June , known as a contango, increased by as much as 20 cents to $1.39 a barrel as news circulated in the market that Transcanada was planning work on its 700,000 barrel per day pipeline.

Two sources who knew about the work said the pipeline, which runs from Cushing, Oklahoma to Texas, would undergo work from April 27 to May 2.

A company spokeswoman confirmed there would be "regularly scheduled maintenance" on the line in May, but did not provide the exact dates for the work or its scope.

The pipeline was also shut for about 24 hours on Friday, the sources said.

The closures fueled concerns about a renewed build-up of inventory in Cushing, Oklahoma, the U.S. storage hub and delivery point for the U.S. futures contract , where inventories are near record highs.

Last month, Cushing inventories peaked at 67.5 million barrels, according U.S. Energy Information Administration data, leading traders to question whether the hub would fill to capacity.

Recent declines in crude stocks signal that the market may be closer to rebalancing, particularly after stocks at the hub fell by 1.8 million barrels last week following a week-long outage on TransCanada's 590,000 bpd Keystone pipeline, which delivers crude from Hardisty, Alberta to Cushing and Patoka, Illinois.

(Reporting by Catherine Ngai and Liz Hampton; Editing by Diane Craft and James Dalgleish)