The discount on benchmark heavy Canadian crude versus West Texas Intermediate held steady on Wednesday.
Western Canada Select heavy blend crude for October delivery settled at $21.00 a barrel under WTI, according to NE2 Canada Inc, unchanged from the previous day.
WCS has been under pressure for much of the summer as a result of the release of predominantly sour crude from the U.S. Strategic Petroleum Reserve (SPR).
Traders are keeping an eye on whether apportionment on Canadian export pipelines will start to increase in coming weeks as production rises, one industry source said. Pipeline apportionment has been low since Enbridge Inc opened its Line 3 expansion late last year, but higher apportionment can weigh on prices if crude gets stranded in Alberta.
There are also concerns about a possible U.S. rail strike that could disrupt crude and refined product shipments south of the border.
Global oil prices edged up 1% as an international energy watchdog expects an increase in gas-to-oil switching due to high prices this winter, even though the outlook for demand remains gloomy.