Most of the above are somewhat irrelevant to the overall question of fuel stability, as ethanol is far from the only added component contributing to the problem. "Pure" gasoline is not a single chemical compound. It has something like 8 major chemical components blended together in varying proportions to achieve a certain number of goals, among which are octane level, oxygenation, emissions reduction, and energy output. Race fuels are usually superior from a performance standpoint, not because of their lack of ethanol so much as their totally different balance of higher energy components in proportion to the more inert parts. Sometimes they can be just as unstable, and anyone who ever dealt with the original formulation of VP's U4 will tell you that. Ethanol started out as a cheap oxygenate, but with the risible fixation with renewable fuels, it became mandated indirectly. MTBE was used in California as an oxygenate, but has fallen out of favor due to its toxicity and its hygroscopic nature. It was turning up in the ground water in places where there had never been a significant spill. On the stability issue, MTBE was not as big a problem as ethanol because it takes less of it to release the same volume of oxygen into the combustion process as ethanol, and while both will bind to atmospheric water, ethanol is better at doing so in the first place, and as mentioned, there is usually more of it than there would be MTBE. Neither of these two are the only component of some of the many fuel blends available in the US that contribute to the instability of fuels stored over time, either, so the ethanol content is not a particularly important point in the discussion. As far as octane goes, several regional blends sporting AKI ratings of 100+ are available in parts of the US, too. In general, one should not expect to be able to store gasoline in a vented container with a lot of airspace for more than 3-4 months at the most, especially in hot weather.