A study on the improvement of the representative operating temperature from the temperature profile of an industrial adiabatic reactor is presented. This temperature is used to simulate the reactor performance by small scale laboratory isothermal reactors. An improved methodology for the estimation of a Weighted Average Bed Temperature (WABT) was elaborated to simulate an industrial multi-bed HDS reactor. The improved WABT, so called Weighted Average Reactor Temperature (WART), was compared with the most usually used WABT in a wide range of operational conditions as well as of kinetic parameters. In case of a multi-bed industrial hydrotreater, where quench zones are located between the beds and the H-2 flow rate, which enters each bed, is different, the optimal gas to oil ratio was estimated for the laboratory-scale reactor. (c) 2005 Elsevier B.V. All rights reserved.