If your generator runs on gasoline or diesel, it’s important to note that these fuels have a relatively short shelf life—about 3-6 months for gas, and 6-12 months for diesel, depending on storage conditions.
Running old fuel in your generator can damage the internal workings, so make sure you’re using relatively new gasoline or diesel. If your generator uses these fuels, store them safely in approved containers. That way, you can rotate old fuel and use it elsewhere before it expires.
Propane has a practically indefinite shelf life, on the other hand.