Gas prices in Sarnia: count more than the exchange rate

Port Huron is right across the river, so most Sarnia drivers have wondered whether filling up in Michigan pays. Sometimes the pump gap looks big. But you’re comparing US dollars per gallon with Canadian cents per litre, and the bridge charges a toll each way. We don’t show live prices; this page gives you the full sum, plus how to get the best result on the Ontario side.

What’s in the price at a Sarnia pump

As of November 2026, a litre of regular in Sarnia includes:

9.0 cents of Ontario gasoline tax, included in the posted price and not itemized on your receipt (Ontario Ministry of Finance).
No federal excise tax for now. The usual 10 cents a litre was suspended on 20 April 2026 and the suspension runs until 31 January 2027, with 5 cents planned for February and March 2027 and the full rate from 1 April 2027 (Department of Finance Canada).
13% HST (CRA), charged on the full pre-tax price including those per-litre taxes (Natural Resources Canada).

What’s in the price at a Port Huron pump

Michigan changed its fuel taxes on 1 January 2026. The state now charges a motor fuel tax of 52.4 US cents a gallon and no longer collects sales tax on fuel (Michigan Department of Treasury; Treasury notice). The rate is indexed to inflation, so it will be reset on 1 January 2027. The US federal gasoline tax is 18.4 cents a gallon (IRS Form 720).

That’s 70.8 US cents a gallon in fixed taxes. A US gallon is 3.785411784 litres (NIST Handbook 44, Appendix C), which works out to about 18.7 US cents a litre before currency conversion. On the Ontario side, the fixed per-litre tax is currently just the 9.0-cent provincial tax, but HST adds 13% on top of everything. The two systems are built differently, so the tax tables alone can’t tell you which side is cheaper on a given day. You need actual pump prices from both, converted properly. Our fuel price converter does the gallon-to-litre and currency step.

The bridge is part of the price

The Blue Water Bridge charges in both directions, and each side sets its own toll:

Into the US: C$7 for a passenger vehicle, or C$4.50 with a Connexion prepaid account, set by the Federal Bridge Corporation (Sarnia News Today, March 2026).
Back into Canada: US$5 for a car since 1 December 2025, collected by Michigan’s transportation department (Global News).

Tolls change, so check both before you go. A fuel-only round trip also means two border inspections and whatever wait there is. We don’t cover customs rules or what you’re allowed to bring back; check those with the border agencies yourself.

Where Sarnia drivers usually fill up

For most fills, the realistic choice is between Sarnia stations on routes you already drive. Esso, for example, lists a station at 121 Indian Road South (checked 4 November 2026; recheck before relying on it). Searchers also look up stations on “the reserve”: Aamjiwnaang First Nation is on the St. Clair River within Sarnia’s city limits (Aamjiwnaang First Nation). Ontario lets eligible First Nations people buy gas without the Ontario gasoline tax at authorized on-reserve retailers by showing a Status Card (Ontario Ministry of Finance). That doesn’t tell you whether a given station is authorized or what price applies to you. Ask the station rather than assuming.

Sarnia isn’t one of the markets in Ontario’s weekly fuel price survey; London and Windsor are the nearest ones it covers. Don’t read their averages as Sarnia prices.

Using GasBuddy Sarnia results

Start with Ontario stations near your route in your grade, and note the report times.
If Port Huron results appear, remember they’re in US dollars per US gallon. Convert both currency and volume before you compare anything.
Add both bridge tolls and the extra distance. If you’re crossing anyway, only count the extra distance to the station.
For an on-reserve station, confirm with the station which price applies to you.
Confirm the pump price before you fill. For current reports, start on the official GasBuddy website.

Sarnia worked example: is a Port Huron fill worth the trip?

This is invented for the arithmetic. It isn’t a quoted price on either side, and the exchange rate is illustrative. Say that after converting, the Port Huron price is 15 cents per litre cheaper, you’ll buy 50 litres, the trip adds 10 km, and US$1 = C$1.40.

Item	Calculation	Result
Gross saving	50 × 15/100	C$7.50
Extra driving fuel cost	10 extra km × 8 L/100 km ÷ 100 × C$1.60 per litre	C$1.28
Bridge tolls, standard rates	C$7.00 + (US$5.00 × 1.40)	C$14.00
Net saving before time and other costs	Gross saving − extra fuel − tolls	−C$7.78

Even with a gap that looks large, the tolls swamp it, and you lose C$7.78 before counting border wait times. With a Connexion account the US-bound toll drops to C$4.50 and the loss shrinks to C$5.28, but it’s still a loss. A fuel-only crossing only starts to make sense when you’re crossing anyway. Try your numbers in the trip fuel cost calculator.

Is gas cheaper in Port Huron than Sarnia?

Converted to Canadian dollars a litre, it sometimes is. Michigan’s tax structure is different from Ontario’s, and prices move independently. But a fuel-only trip pays two bridge tolls, so the pump gap has to be very wide before it covers them.

Does a “reserve” price apply to everyone?

Not necessarily. Ontario’s gas tax exemption applies to eligible First Nations purchasers at authorized on-reserve retailers. Ask the station which price you’ll pay.

More Sarnia fuel planning

Ontario gas prices hub
Convert US$/gallon to C$/litre
London, Ontario gas prices if you drive east regularly
Compare prices near your actual location
Calculate the fuel cost of your route
Check your vehicle for recalls before a long trip

Fuel Route Guide is an independent publication and is not affiliated with GasBuddy or the fuel retailers mentioned here. Illustrative calculations were prepared for this guide; no station visit or live-price verification is claimed.