Diesel is the story of September. As of September 30, 2026, the average price of diesel at the six Costco gas bars we track in Canada that sell it is 245.7¢ a litre — up 39.8¢, or 19.3%, from 205.9¢ on September 1. Regular rose too, by less: across all 78 gas bars it finished at 172.4¢, up 7.5¢ (+4.5%), after peaking at 180.2¢ on September 19. The Prairies that led August lower reversed hard — Saskatchewan up 38.7¢ — while Ontario was flat. Compare a month of rising prices in the U.S., the UK, and Australia.
| Grade | September 1 | September 30 | Month change |
|---|---|---|---|
| Regular | 164.9¢ | 172.4¢ | ▲ 7.5¢ (4.5%) |
| Premium | 187.6¢ | 194.9¢ | ▲ 7.3¢ (3.9%) |
| Diesel | 205.9¢ | 245.7¢ | ▲ 39.8¢ (19.3%) |
National averages of posted prices at tracked Costco gas bars in Canada, ¢/L. Snapshot of calendar September 2026 — this article is not updated.
A steady climb, a jump on September 19, then a partial retreat
Regular climbed in small steps from 164.9¢ on September 1 to 170.5¢ by September 8, edged into the low 170s mid-month, then took its biggest step: from 173.1¢ on September 17 to 180.2¢ on September 19, the high of the month. From there it eased for most of the last ten days and closed at 172.4¢ — 7.8¢ off the peak but still 7.5¢ above where September began. Of 78 gas bars, 55 finished dearer, 21 cheaper, and 2 unchanged.
Diesel had no such retreat until the very end. The six-bar average crossed 230¢ on September 15, 240¢ on September 19, and peaked at 255.2¢ on September 24 before slipping to 245.7¢. Premium tracked regular, up 7.3¢ (+3.9%) to 194.9¢.
The Prairies flipped; Ontario barely moved
Last month Saskatchewan was the cheapest province we track. This month Saskatchewan's Costco average rose 38.7¢(+28.2%) to 175.6¢. Regina added 45¢, from 131.9¢ to 176.9¢ — the biggest station move in the country — with Saskatoon up 36¢ and South Saskatoon up 35¢. All three Winnipeg bars rose 20–22¢ to 166.9¢, and Alberta added 13.2¢. In British Columbia, Kelowna — August's biggest faller — rose 33¢ and Kamloops 20¢, even as Langley cut 10¢. Ontario was the counterweight: up just 0.1¢ on average, with Ajax down 14¢ and North Oshawa down 8¢. Seven of the eight biggest station fallers were in Ontario.
Biggest risers
| Province | Avg now | Change |
|---|---|---|
| Saskatchewan | 175.6¢ | ▲ 38.7¢ (28.2%) |
| Manitoba | 166.9¢ | ▲ 20.7¢ (14.1%) |
| Alberta | 158.1¢ | ▲ 13.2¢ (9.1%) |
| Newfoundland and Labrador | 207.9¢ | ▲ 13.0¢ (6.7%) |
| British Columbia | 184.5¢ | ▲ 9.6¢ (5.5%) |
Smallest moves
| Province | Avg now | Change |
|---|---|---|
| New Brunswick | 188.9¢ | ▲ 9.5¢ (5.3%) |
| Quebec | 183.3¢ | ▲ 3.9¢ (2.2%) |
| Ontario | 168.7¢ | ▲ 0.1¢ (0.1%) |
No province fell on average. Ontario was effectively flat.
September moves by province-average price of regular at Costco, September 1 – 30, 2026.
Every province, ranked by September 30's Costco average
Alberta is now the cheapest province by a clear margin, and 49.8¢ a litreseparates its 158.1¢ from Newfoundland's 207.9¢. The ten cheapest Costco pumps in the country on September 30 were all in Alberta, led by Southwest Calgary at 145.9¢ — 62¢ below St. John's, now the priciest bar we track. Saskatchewan dropped from first to fourth. On the West Coast, Langford at 193.9¢ replaced Langley as British Columbia's dearest pump.
| Province | Gas bars | Costco avg (regular) |
|---|---|---|
| Alberta | 17 | 158.1¢ |
| Manitoba | 3 | 166.9¢ |
| Ontario | 27 | 168.7¢ |
| Saskatchewan | 3 | 175.6¢ |
| Quebec | 17 | 183.3¢ |
| British Columbia | 8 | 184.5¢ |
| New Brunswick | 2 | 188.9¢ |
| Newfoundland and Labrador | 1 | 207.9¢ |
Province-average price of regular across tracked Costco gas bars, September 30, 2026.
Why the Prairies spiked — and why diesel ran furthest
The first half of the month was a crude story. By September 9, Brent was back above US$100 a barrel as fighting in the Middle East escalated and Ukrainian strikes hit Russian refineries; GasBuddy's Patrick De Haan warned the usual post-Labour Day drop and the switch to cheaper winter gasoline might not deliver much relief this year. That is the slow climb in the chart.
The jump was regional. ExxonMobil's Joliet, Illinois refinery — about 275,000 barrels a day — lost power on September 13 and was still offline days later after flooding. The outage reached the Prairies within days: Edmonton and Calgary pumps jumped by as much as 30¢ on September 16, and Dan McTeague of Canadians for Affordable Energy put the hit at roughly 18¢ for gasoline and 24–25¢ for diesel. The same shape is in our data — Regina, Saskatoon, and Winnipeg top the risers table, and the national Costco average stepped up 7¢ between September 17 and 19 — while Ontario barely moved.
Diesel had both problems at once. Russian export limits and refinery damage pushed diesel margins to records, and Kalibrate data showed a record national average of 275.1¢ in mid-September. By the week ending September 29, Natural Resources Canada had retail diesel at $2.64, up about 59% from before the Iran war and 15% above the 2022 record. Costco's six diesel bars, at 245.7¢, finished below that national figure — but still up 19.3% in a month.
The tax holiday didn't end after all
Last month we flagged the federal excise holiday's early-September expiry as the biggest risk. On September 2, Ottawa extended the full suspension to January 31, 2027, with half rates (5¢ gasoline, 2¢ diesel) from February 1 and full rates from April 1. So September's 7.5¢ rise in regular — and the 39.8¢ jump in diesel — happened with the 10¢ and 4¢ cuts still in place. None of it was tax.
What to expect in October
One relief is already locked in: Alberta's 13¢/L provincial fuel tax is suspended from October 1 to December 31, triggered because WTI averaged US$90.54 over the August 18 – September 15 review window. Alberta was already the cheapest Costco province at 158.1¢; if that cut passes through, the country's lowest pumps should drop further. Elsewhere, the late September easing in regular — 7.8¢ off the peak — suggests the Joliet shock is fading at the pump, but crude back above US$100 in mid-September and record diesel margins leave little room for a return to September 1 levels. Diesel is the grade to watch: the six-bar average slipped 9.5¢ from its September 24 high, but freight and farm users are still paying near record prices.
Costco pump prices are a snapshot of calendar September 2026 (September 1–30) and will differ at the pump today. No price snapshot was recorded for September 18; the chart and peak/trough figures skip that day. One GasBuddy premium reading arrived in dollars per litre rather than cents and was rescaled to ¢/L before averaging. This site is independent and not affiliated with Costco Wholesale Corporation.
