Gasoline.
Even treated gas will only last reliably for 12-24 months in well sealed
containers. High octane, alcohol free fuels will do the best.
Diesel.
Diesel can store well for up to 10 years in sealed containers. Treating it
is a good idea. Biocide and anti-oxidant. #2 Non-biodiesel is the best but
may have gelling issues in colder weather.
I am upgrading all my primary equipment to diesel engines. Lister and
Listeroid engines are good back ups.
This should arrive Wednedsay.
http://www.millerwelds.com/products/enginedriven/product.php?model=M00186
Upgrading from my Trailblazer 302 gas engine, that unit is already sold.
both have 10kW of aux power, I regularly back feed my house or shop as
needed when the power fails.
BTW, I am a chemist and work for
http://www.aftonchemical.com/Pages/Home.aspx