The tax cut ended, and the chart shows the night it happened. As of August 31, 2026, Unleaded 91 across the seven Costco stations that post it averaged $1.918 a litre — up 11.1¢, or 6.2%, from $1.807 on August 1. Almost all of that jump landed on August 3–4, when the temporary fuel-excise cut expired at midnight. E10, the 91-RON grade at the other seven warehouses (NSW and Queensland), rose 9.1¢ (+5.1%) to $1.878. Diesel, at all 14 stations, climbed 17.3¢ (+7.7%) to $2.407. Every tracked pump got more expensive. It is the inverse of the July report, when diesel led a fall, and it sits next to a mixed month in the U.S., Canada, and the UK.
| Grade | August 1 | August 31 | Month change |
|---|---|---|---|
| Unleaded 91 | $1.807 | $1.918 | ▲ 11.1¢ (6.2%) |
| E10 | $1.787 | $1.878 | ▲ 9.1¢ (5.1%) |
| Premium 98 | $1.993 | $2.148 | ▲ 15.6¢ (7.8%) |
| Diesel | $2.234 | $2.407 | ▲ 17.3¢ (7.7%) |
National averages of posted prices at tracked Costco fuel stations in Australia, $/L. Unleaded 91 is posted at 7 stations; E10 at the other 7 (NSW and Queensland). Snapshot of calendar August 2026 — this article is not updated.
The August 3 step, then a price cycle on top
Unleaded 91 sat at $1.807 on August 1 and 2, jumped to $1.856 on August 3 and $1.936 on August 4 — a 13¢ two-day step that matches the 16¢/L wholesale snap-back when the excise cut ended at midnight. A city price cycle then took over: a drift down toward $1.86 by mid-month, a second lift to $1.92 around August 22, and a close at $1.918. Diesel followed the same step (2.234 → 2.337 by August 4) without as much cycle, and finished the month near its high at $2.407.
Every state rose; Victoria led
Ranked on 91-RON — Unleaded 91 where the warehouse posts it, E10 in NSW and Queensland — Victoria climbed 12.7¢ (+6.9%), the most of any state. Ardeer and Epping each added 14¢, the biggest station moves on the network. Western Australia, Queensland, South Australia, and the ACT each rose 10¢. New South Wales rose the least, 8.5¢, because Lake Macquarie's E10 only added 4¢. Perth Airport and Casuarina at $1.867 are the cheapest 91-RON fills; Ardeer and Moorabbin at $1.967 are the dearest Unleaded 91.
| State | Stations | 91-RON now | Month change |
|---|---|---|---|
| Victoriabiggest riser: Ardeer | 3 | $1.954 | ▲ 12.7¢ (6.9%) |
| Western Australiabiggest riser: Casuarina | 2 | $1.867 | ▲ 10.0¢ (5.7%) |
| Queenslandbiggest riser: Ipswich | 3 | $1.887 | ▲ 10.0¢ (5.6%) |
| South Australiabiggest riser: Adelaide | 1 | $1.887 | ▲ 10.0¢ (5.6%) |
| ACTbiggest riser: Canberra | 1 | $1.947 | ▲ 10.0¢ (5.4%) |
| New South Walesbiggest riser: Marsden Park | 4 | $1.872 | ▲ 8.5¢ (4.8%) |
August movers by state-average 91-RON at Costco (Unleaded 91 or E10), August 1 – 31, 2026. Every state rose.
Every state, ranked by August 31's Costco 91-RON
The spread across the six states and territories we track is 8.7¢ a litre— Western Australia's $1.867 against Victoria's $1.954. That is tight by Australian standards; the excise step lifted the whole country together, and the city cycles on top have not yet reopened a wide gap.
| State | Stations | Costco 91-RON |
|---|---|---|
| Western Australia | 2 | $1.867 |
| New South Wales | 4 | $1.872 |
| Queensland | 3 | $1.887 |
| South Australia | 1 | $1.887 |
| ACT | 1 | $1.947 |
| Victoria | 3 | $1.954 |
State-average 91-RON (Unleaded 91 or E10) across tracked Costco fuel stations, August 31, 2026.
Why prices jumped on August 3
The temporary fuel-excise cut that had been holding Australian pumps down ended at midnight on August 3, adding about 16¢/L back onto wholesale. Costco Unleaded 91 moved 13¢ in two days; E10 moved a similar step. That is tax, not crude. The rest of the month is the usual east-coast price cycle riding on top of a higher floor — the mid-month drift toward $1.86 and the late-month lift back to $1.92. Diesel has no cycle and a larger product crack, which is why it rose 17.3¢ and finished near the month's high.
Motorist groups had warned of unleaded toward $2.20 and diesel toward $2.60 once the cut lapsed. Costco's $1.92 Unleaded 91 and $2.41 diesel are still well under those forecasts — the club discount held through the step — but they are 11¢ and 17¢ above the August 1 starting line.
The cheap litre of July is gone
July's Unleaded 91 trough was $1.43. August opened at $1.81 and closed at $1.92 after a legislated 16¢ wholesale step. There is no remaining excise cut to unwind. What happens next is the city cycle and Hormuz product cracks, not another tax date.
Will fuel prices keep rising?
The tax step is done. The east-coast petrol cycle will keep swinging 10–20¢ around the new floor, which is why a mid-month dip to $1.86 does not undo an August 4 print of $1.94. Diesel is less cyclical and more exposed to global distillate — the same grade that led July's 10% drop led August's 7.7% rise. Perth Airport and Casuarina at $1.867 remain the cheapest Costco 91-RON in the country; Victoria is where the cycle has run furthest.
Costco pump prices are a snapshot of calendar August 2026 (August 1–31) and will differ at the pump today. This site is independent and not affiliated with Costco Wholesale Corporation.
