According to the FAQs on GoldEagle.com Sta-Bil fuel stabilizer has a shelf life of 2 years after it has been opened. They mention that it is not as effective to use an ‘old’ bottle. I take that to mean it maintains effectiveness for 2 years, after that it doesn’t work as well. https://www.goldeagle.com/product/sta-bil-fuel-stabilizer/
