Paraffins are straight or branched-chain hydrocarbons (ie they do not contain naphthene or aromatic rings).

In a refinery, a paraffinic hydrocarbon will tend to crack well in a cracking unit (eg FCC), and will have a higher cetane when blended into diesel, especially if it contains more straight chains and fewer branches. Likewise, it will tend to perform poorly in a reformer and would make a poor (low octane) gasoline blend stock.