The Energy Resources Conservation Board said the oil emptied out of the Plains Midstream Canada Rainbow pipeline Friday about 63 miles northeast of Peace River, The Globe and Mail reported.
The provincial energy regulator called it the largest pipeline leak in Alberta since 1975, the Toronto newspaper said.
"It's certainly a very significant leak," said Davis Sheremata, a board spokesman.
The last time the 45-year-old Rainbow pipeline leaked was 2006 when 7,500 barrels escaped. The Alberta pipeline, which extends 480 miles from Zama to Edmonton, is designed to carry 220,000 barrels per day and last year averaged 187,000 barrels.
The Globe and Mail said crews had to build several miles of road to gain access to the latest spill.
Most of the oil was contained on the pipeline right-of-way, though some reached a nearby wetland, the regulator said. None has reached running water.
The spill was detected by Plains Midstream crews, the board said.