Two Australian forces collided this month, and the chart shows both. As of July 10, 2026, the average price of Unleaded 91 across the 14 Costco fuel stations we track is $1.527 a litre — down just 3.4¢, or 2.2%, from $1.561 a month ago. That tiny net move hides a full price cycle: unleaded slid to a $1.427 trough around July 1 — the cheapest in the window — then jumped about 10¢ in days as the cycle turned and part of the fuel-tax cut lapsed. Diesel, which has no cycle, tells the cleaner story: down 19.4¢, or 10.1%, to $1.736, the biggest 30-day drop of any grade. It is the same bottom-and-bounce we found across the U.S., Canada, and the UK this month — with an Australian tax twist on top.
| Grade | June 11 | July 10 | 30-day change |
|---|---|---|---|
| Unleaded 91 | $1.561 | $1.527 | ▼ 3.4¢ (2.2%) |
| E10 | $1.553 | $1.500 | ▼ 5.3¢ (3.4%) |
| Premium 98 | $1.781 | $1.740 | ▼ 4.1¢ (2.3%) |
| Diesel | $1.930 | $1.736 | ▼ 19.4¢ (10.1%) |
National averages of posted prices at tracked Costco fuel stations in Australia, AUD/L. Costco stations carry either Unleaded 91 or E10 depending on the site. Snapshot taken July 10, 2026 — this article is not updated.
A textbook price cycle — trough on July 1, then the turn
The unleaded line is the most Australian shape in this whole series. It fell in a near-straight line for three weeks — more than 13¢ — to a floor of $1.427, held from June 28 to July 1, then snapped about 10¢ higher in the first days of July: the down-slope and sharp V-turn of a capital-city price cycle bottoming out. Diesel, which doesn't cycle, fell cleanly to a $1.618 low on July 1 and has since drifted back to $1.736 — a rebound driven by crude and tax rather than the retail cycle.
Queensland fell hardest; the west is cheapest
Measured trough-aware across the full window, Queensland cut its state average by 8¢ — Ipswich and North Lakes led with 9¢ each — while Western Australia, Victoria, and New South Wales trimmed 3–4¢ net after the cycle bounce ate into the earlier falls. Casuarina, WA is the cheapest Costco pump in the country at $1.427, and Western Australia the cheapest state at $1.447; Canberra, at $1.627, remains the priciest. The full network spread is 18¢.
| State | Stations | Avg now | 30-day change |
|---|---|---|---|
| Queenslandbiggest faller: Ipswich | 3 | $1.494 | ▼ 8.0¢ (5.1%) |
| Western Australiabiggest faller: Casuarina | 2 | $1.447 | ▼ 4.0¢ (2.7%) |
| Victoriabiggest faller: Epping | 3 | $1.550 | ▼ 3.7¢ (2.3%) |
| New South Wales | 4 | $1.504 | ▼ 3.2¢ (2.1%) |
Biggest 30-day fallers by state-average price of Unleaded 91 at Costco, June 11 – July 10, 2026. South Australia and the ACT have a single station each, so they are ranked below but not compared here.
Every state, ranked by today's Costco average
| State / territory | Stations | Costco avg (Unleaded 91) |
|---|---|---|
| Western Australia | 2 | $1.447 |
| Queensland | 3 | $1.494 |
| New South Wales | 4 | $1.504 |
| South Australia | 1 | $1.517 |
| Victoria | 3 | $1.550 |
| ACT | 1 | $1.627 |
State-average price of Unleaded 91 (or E10 where carried) across tracked Costco stations, July 10, 2026, cheapest first. See every station on the live Australia map.
Why prices bottomed — and the tax twist on July 1
Australia's autumn spike is unwinding fast. After the United States and Israel went to war with Iran and Iran closed the Strait of Hormuz, capital-city petrol blew past $2.50 a litre and diesel well over $3. Two forces have drained most of that: crude collapsed after the June reopening of the strait, and the ACCC notes that since April 1, retail petrol across the five biggest cities is down about 39% and diesel about 44%. That is the leg down to the July 1 trough on our chart.
The turn back up is where Australia diverges. Two things lifted pumps in early July at once. The price cycle bottomed and rolled over — a domestic retail rhythm, not a crude signal. And the tax cut shrank: the deeper relief that had more-than-halved fuel excise from April to June lapsed on June 30, and Canberra replaced it with a smaller extension worth about 16¢ a litre for July, saving roughly $11 a tank. So the June report's cliffhanger — a 32¢ cliff at midnight on June 30 — landed softer than feared: part of the relief rolled off, not all of it, which is a chunk of the early-July rise you see here.
Diesel's 19¢ fall is the war premium still deflating. Australia imports more than 90% of its fuel, much of it from Asian refineries that run on Hormuz crude, so diesel spiked hardest and had the most to give back. Its early-July uptick — from $1.618 to $1.736 — is the same crude rebound and partial-excise return that lifted petrol, minus the retail cycle. Even after the fall, the ACCC notes diesel is still slightly above its pre-war level, and the NRMA warns that with the strait's refineries damaged, a return to sub-$1.80 unleaded is still some way off.
A caution before you extrapolate the chart
Both lines end pointing up, and both reasons can keep pushing. The price cycle has only just turned, so unleaded may climb further before its next down-leg. And the July excise extension is exactly that — a one-month measure; the government has flagged it will reassess as the cut-off nears, so an August change could add more. On top of both sits the same wildcard as everywhere else: a shaky U.S.–Iran ceasefire nudged crude back up in early July, and Australian bowsers run a week or two behind it.
How Costco compares with the servo down the road
The club discount is doing its usual work. The NRMA puts the Sydney unleaded average near $1.99 a litre for July— about 40¢ above pre-war — while Costco's four New South Wales sites average $1.504, roughly 49¢ under that citywide figure. The pattern repeats nationally: Costco's state averages sit in the $1.45–1.55 band while the ACCC's capital-city averages run well into the $1.80s and beyond. As we saw in the U.S., Canada, and the UK, the gap widens in a volatile market — and Costco fuel is members-only.
Will prices keep rising?
Short term, two Australian mechanics point up regardless of oil: the price cycle has just turned, and the July excise extension is only guaranteed for the month. The ACCC's cycle tips are the best near-term guide to whether to fill up now or wait a week. Further out, it is the strait again: the EIA assumes Hormuz shipping keeps recovering, which would keep crude — and eventually Australian pumps — easing, but the early-July rebound shows how quickly a fragile ceasefire can reverse that. The one certainty is the calendar: whatever Canberra decides about the excise for August lands straight on the bowser.
Costco pump prices are a snapshot observed July 10, 2026 and will differ at the pump today. This site is independent and not affiliated with Costco Wholesale Corporation.
