The price of Western Canadian Select (WCS) crude fell to a record US$52.50 per barrel below the price of Northern American benchmark West Texas Intermediate in trading Thursday, according to Net Energy, Calgary-based oil traders whose records go back to early 2007.

Similarly, Thursday’s WCS differential is a record using Bloomberg data, which goes back to 2008.

A shortage of pipeline capacity and refinery maintenance have combined to cause a growing glut of crude in Alberta, making Canadian oil cheaper relative to the U.S. benchmark. Alberta Premier Rachel Notley complained last week that widening price differentials are costing Canadian producers and governments upward of $40-million a day.

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Read more: Price of Canadian heavy oil hits 10-year low compared with benchmark WTI crude