Extra fuel is one of the most misunderstood pieces of overlanding gear. Plenty of rigs roll around with two jerry cans bolted to the swing-out that have never been opened, while other drivers head into genuinely remote country with nothing but a half tank and optimism. Both approaches are wrong. This guide covers when you actually need extra fuel, how to calculate how much, which containers are worth buying, and where to mount them so you are not turning your rig into a hazard.
Do You Actually Need to Carry Extra Fuel?
For most trips in the lower 48, the honest answer is no. If your route keeps you within 100 miles of a gas station and your rig has a 300 mile range, extra fuel is dead weight. Fuel is heavy: gasoline weighs about 6.3 pounds per gallon, so two full 5 gallon cans add over 70 pounds with the containers, usually mounted high and far from the axles where weight hurts handling most.
You do need extra fuel when any of these apply:
- Long remote stretches. Routes like the White Rim Trail, portions of the Mojave Road, Big Bend backcountry, or long BLM corridors in Nevada and New Mexico can put 150 to 250 miles between reliable pumps.
- Off-road fuel economy collapse. A truck that gets 18 mpg on the highway can drop to 8 to 10 mpg in sand, deep mud, or low range rock crawling. Your trip math has to use trail mpg, not window sticker mpg.
- No bailout options. If the only exit from a route is the way you came, you need enough fuel for the round trip plus reserve, not just the distance on the map.
- Small tanks. Two door Wranglers, older Tacomas, and many SUVs have 17 to 21 gallon tanks. Their real trail range can be under 200 miles.
How Much Extra Fuel to Carry: The Math
Skip the guesswork and run this calculation for every remote route:
- Total trail miles between reliable fuel stops. Use your mapped route, not straight line distance.
- Divide by your worst case trail mpg. If you do not know it, assume half your highway mpg for sand, mud, or sustained low range work, and about two thirds for graded dirt.
- Add a 25 to 30 percent reserve for detours, getting stuck, winching, running the engine at camp, or helping someone else.
- Subtract your usable tank capacity. Whatever is left is what you carry.
Worked Example
A 4Runner with a 23 gallon tank averaging 11 mpg on a hard route has roughly 250 miles of range. For a 220 mile remote loop, a 30 percent reserve pushes the requirement to 286 miles, or 26 gallons. That is a 3 gallon shortfall, so one 5 gallon can covers it with margin. Two cans would just be ballast.
Diesel owners get more slack. Diesel rigs typically lose a smaller percentage of their economy off-road, and diesel is safer to transport because it is far less volatile than gasoline. The same math applies, but the reserve you need is usually smaller.
Fuel Container Types Compared
NATO-Style Steel Jerry Cans
The 20 liter (5.3 gallon) steel NATO can is still the benchmark. Genuine NATO-spec cans (Wavian, Valpro, and similar) have a fully welded body, an internal breather tube for smooth fast pours, and a cam lever bail handle that seals against a replaceable gasket.
Pros: extremely durable, excellent vapor seal, handles pressure swings from temperature changes, pours 5 gallons in under a minute with the right spout, decades of service life.
Cons: heavy (about 10 pounds empty), around 45 pounds full, needs a dedicated mount, quality cans run $80 to $100 before the spout.
Avoid cheap steel lookalikes with pin-hinge lids and thin gaskets. The seal is the whole point.
Plastic DOT/CARB Cans
Modern plastic cans from Scepter, No-Spill, and similar brands are lighter and cheaper. Scepter's military-style plastic cans are a legitimate middle ground and are standard issue in several militaries.
Pros: lighter, cheaper, no rust, no paint damage worries.
Cons: UV exposure degrades plastic over years, cans swell visibly in heat, bargain-bin versions with "spill proof" nozzles pour painfully slowly and crack at the welds.
If you go plastic, buy the military-style Scepter, not the $25 hardware store can.
RotoPax
RotoPax are flat, rotomolded packs that bolt to a proprietary mount and stack in 1, 2, 3, and 4 gallon sizes. They exist because they package where nothing else fits: flat against a tire carrier, on a roof rack crossbar, or on the back of a side-by-side.
Pros: slim profile, modular, excellent mounting hardware, good seal.
Cons: cost per gallon is roughly double a jerry can. A 2 gallon RotoPax costs about the same as a 5.3 gallon steel can. The packs also swell noticeably in summer heat, and pouring is slower.
The honest use case for RotoPax is space-constrained mounting, small vehicles, or carrying 2 to 4 gallons as insurance. If you need 10 gallons regularly, jerry cans win on cost and pour speed.
Auxiliary and Replacement Fuel Tanks
If you carry extra fuel on most trips, stop strapping cans to the outside and look at a long range tank. Companies like Long Range America and ARB's OME-adjacent partners offer replacement or auxiliary tanks for popular platforms (Tacoma, 4Runner, Wrangler, LandCruiser, Super Duty) that add 10 to 24 gallons below the body.
Pros: weight sits low and centered, fuel is plumbed into the vehicle, nothing to unstrap and pour, no theft or vapor issues.
Cons: $1,500 to $3,500 installed, platform-specific availability, may complicate spare tire or exhaust routing.
The break-even is simple: four jerry cans plus mounts and a swing-out reinforcement can run $600 to $1,000 and cost you handling. If extra fuel is a lifestyle rather than a once-a-year event, the tank is the better build decision.
Fuel Bladders: Mostly Skip
Collapsible fuel bladders exist for expedition use, but most are not DOT approved for gasoline in the US, they are vulnerable to chafe, and a failure is catastrophic. For typical North American overlanding they solve a problem you do not have.
Where to Mount Fuel Cans (Best to Worst)
- Rear bumper swing-out or tire carrier. The standard answer. Weight is behind the axle but low, cans are accessible, and purpose-built carriers lock. Make sure your swing-out is rated for the load; 90 pounds of fuel slamming on washboard will find weak welds.
- Hitch-mounted carrier. Cheap, easy, keeps fuel out of the cabin airspace, and the weight sits low. Downsides: it kills your departure angle, extends your rig, and cans are exposed to rear impacts. Fine for graded roads and mild trails.
- Truck bed. Excellent if you have one. Strap cans upright to the bed wall with the spout up, away from cargo that can shift into them. Never transport cans loose, and never fill a can sitting in a plastic bedliner or on the tailgate; static discharge during filling is a real ignition source. Always place cans on the ground to fill them.
- Roof rack. Last resort for gasoline. It raises your center of gravity by 45 pounds per can at the worst possible height, sun exposure cycles the can through expansion and contraction daily, and any leak runs down your paint and window seals. If you must, use steel NATO cans with fresh gaskets, mount them upright in locking holders, and check them at every stop. Water and diesel belong on the roof before gasoline does.
Never Inside the Cabin
Never mount or store gasoline inside a cabin or enclosed SUV cargo area. Gasoline vapor is heavier than air and accumulates. Even a sealed can vents in heat. If an enclosed vehicle is your only option, it is the wrong trip to carry extra gasoline.
Safety and Legal Basics
- Use DOT/UL/ASTM approved containers with capacity of 5 gallons or less for portable use. Anything bigger is not a portable can under US rules.
- Leave headspace. Fill cans to about 95 percent. Gasoline expands with heat, and a can filled to the brim on a cool morning will be pressurized by noon.
- Ground the can when filling. On the ground, nozzle in contact with the can. Never fill in the bed or on carpet.
- Check gaskets seasonally. Most jerry can leaks are dead gaskets, and replacements cost a few dollars.
- Rotate your fuel. Untreated gasoline starts degrading in about three months. Either empty carried cans into your tank at the end of each trip, or treat the fuel with stabilizer and cycle it every few months. Do not let a can sit full through a whole season and then count on it.
- Label diesel vs gasoline clearly. Standard color code: red for gasoline, yellow for diesel, blue for kerosene, and keep water cans visually distinct (typically white or blue with clear labeling). Pouring the wrong fluid 150 miles from pavement turns an inconvenience into a recovery operation.
Common Mistakes
Carrying fuel instead of planning fuel. Cans are not a substitute for route planning. Know where the reliable pumps are, and treat small town single-pump stations as unreliable; they close early, run dry, and lose power.
Using highway mpg for trail math. This is the single most common cause of range surprises. Sand can cut your economy by more than half.
Buying mounts before cans. Pick the container that fits your fuel math, then buy the mount. Plenty of people buy a swing-out with two can trays and then feel obligated to fill them.
Ignoring the weight budget. Two full jerry cans, a full 5 gallon water can, and a loaded swing-out can add 200 pounds behind the rear axle. If you just read a payload sticker for the first time recently, count your fuel in that math.
Storing cans full in the garage. Vapor plus a water heater pilot light is how garages burn down. Store fuel in a detached shed or outside a living structure, out of the sun.
Quick Recommendations
- Weekend trips near civilization: carry nothing, keep your tank above half.
- Occasional remote routes, most rigs: one or two 20 liter NATO steel cans on a rated rear carrier. This covers 90 percent of overlanders.
- Small vehicles and tight packaging: RotoPax in the size your math requires, mounted flat where a jerry can will not fit.
- Frequent long range travel: an auxiliary or long range replacement tank. It is the most expensive option up front and the cheapest per trip.
The Bottom Line
Run the math for every remote route: trail miles divided by worst case mpg, plus 30 percent, minus your tank. Carry only the difference in approved containers, mounted low and outside the cabin, and rotate the fuel so it is fresh when you finally need it. Extra fuel should be a calculated answer to a specific route, not a permanent fashion accessory bolted to your bumper.