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Re: Octane rating Drop (Kirb)

Well, there's not really much truth there, but there are a couple of things that can happen to gas.

1) Moisture can work it's way into the gas as it ages. This is obviously not good.

2) If the gas has ethanol in it, the ethanol likes to go bond with water. If there is excessive moisture in any of the receiving tanks, the ethanol could come out of suspension and bond with the water, changing the chemical composition and dropping the octane rating.

3) If the gas sits in an open container, the higher order hydrocarbons will volatize off, changing the composition and lowering octane.

HOWEVER, all of the above is EXTREMELY insignificant and rare if you go to a station that has ANY volume at all. Most busy city stations get deliveries every 24-48 hours. Depending on the station, that means that they go through 5,000 to 25,000 gallons per day. Some popular stations off the highways even go through 40,000 GPD.

Also, any major gas station you go to does it's best to ensure that the tanks are tight, including atmospheric emissions. Therefore, the chances of volitazation happening are extremely rare.

Moisture making it in is somewhat more likely, but not very. Plus the connection between the truck and the tank is sealed (i.e. it's not just a hose in a hole like when you fill your tank) and there's not much chance of anything happening there. When you fill your tank, it's not really closed, but the volume of fuel going in vs. the relative area of air it contacts makes any volatization very very unlikely.

If you feel like you got a bad batch of gas, chances are it was contaminated in some way, rather than it was "old" or "stale"

Bottom line, if you don't keep cans in your garage or a tank at your house, and if you live in a relatively populated area with a relatively busy station, you're fine. If you put gas in a plastic container that was bone dry and very air tight, it would have a pretty long shelf life. In a more open container like a gas can for your lawn mower, yes, gas will have a shelf life. However, the moisture that makes it way in and the higher hydrocarbons that make their way out won't really matter to your lawn mower. But don't throw it in your car and expect it to run really well.
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