I thought I'd share what Chevron claims about the shelf life of the newer "reformulated gasolines". They claim they have better storage charactaristics than the previous fuels..."
"Federal and California reformulated gasolines will survive storage as well or better than conventional gasolines. The regulations require reformulated gasolines to have less light ends and less olefins (federal, later; California, now) than conventional gasolines. As explained above, it is the oxidation of olefins that leads to gum formation. Reformulated gasolines also contain oxygenates. The common oxygenates are stable molecules that do not form gums.
A larger volume of gas will be pumped in and out of the container when the air space above the liquid fuel is larger and when the daily temperature change is larger. Consequently, keeping the container almost full of gasoline and controlling the temperature fluctuations will minimize the loss of light ends, the exposure of the gasoline to air, and the contamination of the gasoline with water.
Most gasolines contain negligible amounts of gum when they are manufactured, and most contain special chemicals ("stabilizers") to retard gum formation. It is the stabilizers that make it possible to store Chevron gasolines for a year when the conditions are good".
From that Chevron link, it further states:
"Formulation changes that have occurred in the past five years â€” the addition of oxygenates and the reduction in benzene and other aromatics â€” have made gasolines more subject to microbial growth. Even if no water is detected, add a biocide to the gasoline in the fuel tank. Follow the label directions. The best mixing is achieved if the biocide is added to the tank before it is filled with gasoline. Biocide additives are available at marinas and boat supply stores."
StarTron claims to have enzymes to help prevent microbial growth:
"Microbial Growth In Fuel"
"When gasoline or diesel fuel sits in a tank with excessive air space, the daily temperature changes produce condensation (water formation) on tank walls. This water falls into the fuel where it sinks to the bottom providing a breeding ground for microbial spores that feed on hydrocarbon fuels. Known as "diesel algae" these are primarily fungi, yeast and mold contaminants. If left untreated, diesel algae will ruin the fuel causing clogs in filters, fuel lines and injectors. Common treatment for this problem up until now has been the use of a biocide to kill existing growth and prevent a future infestation. The use of a biocide can however cause other problems. Once the growth is killed, the resulting biomass settles to the tank bottom where it decays forming organic acids. The acids then deteriorate the fuel and cause corrosion of the tank walls, injectors and fuel delivery system. Additionally, biocides can be harmful to all those who handle them or come in contact with treated fuel, plus they can cause environmental damage if spilled. Star TronÂ® uses its nontoxic enzyme technology to disperse microbial growth throughout the fuel. These microbial particles are then either safely burned away or filtered out."