How low has your gas prices become?

[glatt]

Well the owner's manual of my lawnmower has detailed instructions of how to put the mower away for the season. Running the tank dry and pumping the primer bulb repeatedly and starting the mower up until every last drop is burnt. Briggs and Stratton doesn't want old gas to sit in the carburetor, because it will gum it up.

The Straight Dope doesn't answer definitively, but says that often gas will only last a couple of months before going bad. Especially gas with ethanol in it.

The shelf life of gasoline depends on the type of gas and the storage conditions and can range from a couple months to a couple years. One wild card is that gas you buy at the pump may already have been in storage for anywhere from days to months.

....

How to keep your fuel April fresh? First, store it only in clean containers with tight caps. Whether the containers are metal or plastic doesn't matter much, although steel can eventually rust. Fiberglass containers should be avoided unless they're rated safe for alcohol-containing fuels. Keep the container nearly full to reduce exposure to air, but not completely full, so the gasoline can expand or contract as the temperature changes. That said, try to minimize those temperature swings--store gasoline in a cool place to reduce evaporation and oxidation. Consider a gas stabilizer for fuel you plan to keep awhile, but remember stabilizers are meant to prevent gasoline from going bad; they won't restore bad gas to its former health.