First, food grade polyethylene barrels are NOT for fuels and oils!
You did not say what you are going to use the tank for or where it would be stored so, make sure you choose a tank that is safe and approved for fuel storage and its intended use by a group like Underwriters Laboratories. Chevron has also posted some storage recommendations at this link.
www.chevron.com/products/ourfuels/prodserv/fuels/technical_safety_bulletins/ltg_storage.aspx
While high-density polyethylene (HDPE) tanks work well for many chemicals (sometimes even motor oil or diesel), they are not well-suited for certain others including chlorinated hydrocarbons such as gasoline, solvents, aromatics, or strong oxidizers. However, some HDPE Fuel and Oil tanks could work in the short-term for gasoline storage but there is a long-term potential for the container to become saturated with fuel, since gasoline is able to permeate HDPE. Essentially, polyethylene should not be used to store gasoline I would get an approved container.
For long-term storage of gasoline, you might want to look into racing fuels. Some racing fuels have close to unlimited shelf life if stored properly. In another thread, contact00 posted this link,
www.vpracingfuels.com, which looks like a better source for race fuel than the one I have used.