In the OIL (gasoline) or in the bottle?
What brand? I would say that every brand has their own different results.
In the fuel... depends on HOW much and How stored, etc. Some will only last a few months, others may several more, still some a year, lastly others a few years with SOME lasting 10+Years. But to be on the safe side it would be best to use up the fuel within it's storage limit time and replenish with more stock!
Per Shell, gasoline stored longer than 6 months may benefit from a stabilzer additive. http://www.countonshell.com/products/product_info/gasoline_faq.html
Based on the Pennzoil and StaBil MSDSs below, these additives appear to be fairly simple formulas, primarily light oil products such as mineral spirits. These formulas appear similar to many fuel system cleaner products, including STP's. http://householdproducts.nlm.nih.gov/cgi-bin/household/search?tbl=type&queryx=Fuel+System
On STP's website, they mention that all their fuel and oil additives have "indefinite" shelf lives. Assuming your product is like the above, it should still be good so long as it was tightly capped, even if several years old.
I had a container of Sta-Bil that I only used a little bit every year. The container (Sta-Bil only, not mixed) lasted quite a few years (4 or 5) and seemed OK.
I've had stabilized gas last over a year and seem OK, although I try not go too much more than a year.
[ January 18, 2004, 10:41 PM: Message edited by: Rick in PA ]
I'm talking about the actual stabilizer itself. I must have 3 or 4 types in my garage and only use it for my lawn equip every winter. I bet some is over 4 years old.
Per the MSDS, the StaBil product is 95% mineral oil. Funny how simple some of these additives are. Blue99 found the "official" answer, although if the stuff is really this unsophisicated, I wouldn't hesitate to go longer: The site below mentions mineral oil as having a 10-15 yr shelf life. http://www.atransformedlife.net/new_page_3.htm
The term mineral oil is one of those dual usage terms that is dependent on the context it is used in. On a MSDS sheet for for a fuel stabilizer, mineral oil is used as a more general petroleum term and probably refers to a light viscosity base oil.
Seems to me the term for mineral oil used in the pharmaceuticals & cosmetics industries is "white mineral oil".