Detailed product distributions from the bifunctional conversion of decane over Pt/ZSM-22, Pt/ZSM-5 and Pt/USY catalysts are compared. In contrast to other zeolites, the product selectivities from decane on Pt/ZSM-22 vary largely with the reaction conditions. Pt/ZSM-22 produces high yields of feed isomers under mild reaction conditions. Molecular graphics suggest that the isomerisation of decane cannot occur entirely inside the micropores of ZSM-22 crystals. It is suggested that isomerisation of decane on ZSM-22 is an example of zeolite pore-mouth catalysis. Type C hydrocracking of methylnonanes (involving beta-scission of secondary into secondary alkylcarbenium ions) does not occur on Pt/ZSM-22, due to the limited access of these molecules in the zeolite pores. Hydrogenolysis on the platinum metal and type D hydrocracking of decane (involving beta-scission of secondary into primary alkylcarbenium ions) account for the formation of cracked products.