If you have a gas station near you which sells ethanol-free gas, I would recommend that. And then add some Techron periodically to clean things out.

You can find a list of ethanol-free gas stations here: Ethanol-free gas stations in the U.S. and Canada

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2006 X5 4.4i
Sport package, summer package, cold weather package, DSP + Nav
Bought 2/14 with 73k miles