No, STA-BIL®Fuel Stabilizer will not restore or improve old gasoline. It will, however, stop it from degrading further. The best thing to do is treat the fuel with STA-BIL® brand as soon as you buy it.
Depending on the quality, type and source of the gasoline, as well as storage conditions, doubling the dosage rate of STA-BIL® brand could prolong this storage time to up to 2 years. However, any gasoline stored for more than 12 months will tend to lose volatility (ignitability), which could lead to hard starting or no start conditions after this long storage period. NO additive, STA-BIL® brand included, will prevent volatility loss in fuel. To reduce fuel volatility loss during storage, we recommend filling your tank at least 95% fulll with fresh fuel and STA-BIL® brand, and store in cool conditions away from direct sunlight if possible.