A pre-reformer (10) comprises a non-electrically conducting gas tight duct (12) and an electrically conducting wire (14) arranged in the duct (12). The electrically conducting wire (14) is electrically isolated from the duct (12). The duct (12) has an inlet (16) for receiving a hydrocarbon fuel at a first end (18) and an outlet (20) for supplying a pre-reformed hydrocarbon fuel at a second end (22). At least the inner surface (24) of the duct (12) is chemically inert with respect to the hydrocarbon fuel. An electrical power supply (26) is electrically connected to the electrically conducting wire (14) and a control means (28) controls the supply of electrical current through the electrically conducting wire (14) to maintain the electrically conducting wire (14) at a temperature to provide selective thermal decomposition of higher hydrocarbons in the hydrocarbon fuel. The performer reduces coking in associated fuel cells and other parts of a fuel cell system.