Isomerization processes have been used to isomerize n-butane to iso-butane used in alkylation and C5 /C6 n-paraffins in light naphtha to the corresponding iso-paraffins to produce high-octane number gasoline stocks after the adoption of lead-free gasoline. Catalytic isomerization processes that use hydrogen have been developed to operate under moderate conditions. Typical feedstocks for isomerization process include hydrotreated light straight-run naphtha, light natural gasoline, or condensate. The fresh C5/C6 feed combined with make-up and recycled hydrogen is directed to a heat exchanger for heating the reactants to reaction temperature. Hot oil or high-pressure steam can be used as the heat source in this exchanger. The heated feed is sent to the reactor. Typical isomerate product (C5+) yields are 97 wt% of the fresh feed, and the product octane number ranges from 81 to 87, depending on the flow configuration and feedstock properties.