Ocean State Oil only sells DEF which is produced according to ISO 22241 standards and is certified by the American Petroleum Institute. Purity of diesel exhaust fluid is important to maintaining a functioning SCR system. Any chemical impurity in DEF can lead to failure of a SCR system. That is why it is very important to use only DEF products that meet ISO 22241 standards and are certified by the API. Calll us or lick on our Diesel Exhaust Fluid page for more info.