Gasoline-powered generators use a fuel that normally is available everywhere. And because smaller gasoline units have onboard fuel tanks, you can move them readily to where you need them.
Major drawbacks relate to the nature of gasoline. It is highly flammable, which makes storing large quantities hazardous.
Gasoline also is relatively expensive, with a short shelf life of only about six months. In widespread power outages, gasoline may not be available because there’s no electricity to power the gas pumps.
Propane offers a long shelf life, up to two years, and can safely be stored in large bulk tanks or portable cylinders. Propane units also tend to run quieter than gasoline units and don’t gum up in storage.
Propane in cylinders may be available during widespread power outages that idle gas pumps. On the minus side, you must keep on hand a pressurized container of flammable fuel that can become dangerous if the container or fuel line is damaged.
And large propane containers are hard or impossible to move. Depending on local prices, propane can also be more expensive per hour of generator operation than gasoline.