This study describes a study of catalysed steam methane reforming. A microreactor of 3 turn bore, operated and controlled by computer has been used. The catalyst employed was an industrial type steam reforming nickel oxide-alumina catalyst containing 15% nickel. The experiments were performed at temperatures of 600-840degreesC. The pressure range was 2.5-9 bar, at hydrogen-to-methane ratio of 0.5-2 and steam-to-methane ratio of 2-3. The catalyst was initially activated at 700degreesC in a flow of steam and hydrogen (7: 1) for 16 h. Subsequent activation methods including hydrogen reduction and temperature treatment were found to have dynamic effects on catalyst activity. An important improvement in the activity of the catalyst at lower temperature was established by incorporating a dynamic sequence of temperature changes that included some experiments at temperatures within the range 750-850degreesC. The dynamics of several such experiments were measured and recorded. The improvement in activity at lower temperature following a high temperature experiments gradually declined at a rate that was much slower than the dynamics of mass transfer and heat transfer in the system. The experimental results were used to examine a dual reaction mechanism for the reforming process. The reaction velocity coefficients established by non-linear parameter estimation were studied as a function of temperature, pressure and composition. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.