alt Hacker NewsFuel goes bad mostly only when mixed with bio fuel, which allows bacteria to grow which does not happen for pure fossile fuel. Additives may degrade, too - but they can be mixed after long term storage. So jet fuel which is basically identical to diesel (except additives) can be stored unlimited.
Petroleum diesel and jet fuel degrade via oxidation, hydrocarbons react with oxygen to form gums, varnishes, and sediments. Biocontent does accelerate degradation but without additives most diesels will be severely degraded at most in 12 months. That’s before we get into water contamination and fun things like Cladosporium resinae.