The right fuel type depends less on the generator and more on how you plan to use it — frequency, duration, and storage all point in different directions.
Gasoline: cheapest generator, worst fuel for long-term storage
Gas generators are typically the least expensive to buy and widely available, but gasoline degrades over months without a stabilizer, making it a poor choice for a generator that sits unused for long stretches waiting for a rare emergency. It's best suited to frequent or planned use where fuel gets rotated regularly.
Propane: indefinite shelf life, lower energy density
Propane never degrades in storage, making it the preferred choice for infrequent, multi-day backup scenarios where the generator might sit unused for a year or more between uses. The trade-off is lower energy density than gasoline — propane generators typically need a larger fuel supply for the same runtime. See the propane tank size calculator and compare against gasoline burn rates in the fuel consumption calculator.
Diesel: most efficient, most common for larger standby units
Diesel generators are generally the most fuel-efficient of the three and are common in larger whole-home standby and commercial applications. Diesel fuel also stores reasonably well (better than gasoline, not as indefinitely as propane) and diesel generators tend to have longer service lives, though they cost more upfront.
Dual-fuel: hedging your bet
Dual-fuel generators that run on either gasoline or propane offer flexibility — use gasoline when it's convenient and propane for long-term storage reliability, switching based on what's available during an actual emergency. This comes at a modest cost and complexity premium over a single-fuel unit.
Frequently asked questions
How long does gasoline actually last in storage?
Untreated gasoline can start degrading within a few months, though fuel stabilizer additives can extend usable shelf life to a year or more — regular rotation is still the most reliable approach for gas stored long-term.
Is diesel worth the higher upfront cost for a home generator?
For larger whole-home standby systems used more than occasionally, diesel's efficiency and longevity often justify the cost — for smaller, infrequent-use backup, the upfront premium may not pay back as clearly.