Fuel compositions

A fuel composition for use in a homogeneous charge compression ignition (HCCI) engine, comprising a gasoline base fuel and one or more additional components selected from the group consisting of (i) a diesel fuel ignition improver, (ii) a Fischer-Tropsch derived gas oil and (iii) a Fischer-Tropsch derived naphtha fuel. Also provided are a process for preparing the fuel composition and its use in an internal combustion engine.