Variable Shelf Life
Clean, properly stored home heating oil is good from 18 months to two years, depending on a few factors. Many oil companies add preservatives that can increase the oil's shelf life. Oil with these preservatives can be useful for up to two years.
Contamination and Spoilage
In many cases, heating oil that might have been useful becomes contaminated. Rust from steel storage drums, water seepage into the oil, or dust and dirt in the oil can make it dangerous to burn. Contamination is a combustion risk; even a small leak of heating oil requires a costly professional cleanup.
Some experts recommend using polyethylene, double-wall storage tanks instead of steel barrels to store fuel. If the oil supplier does not already use preservatives, additives are available that can extend the life of stored oil.