A design procedure for tubular reactors is developed for liquid-phase reactions with gas release in horizontal tubes of small diameters. It is based on a one-dimensional calculation approach, which assumes a stationary turbulent flow. For each stream-wise position on the tube axis, the model delivers the actual temperature, void fraction, chemical composition and slip of the mixture. The possible retardation of the gas release from the liquid proves to be a decisive factor. Approaches to handle this phenomenon are described. The calculation of the tubular flow reactive system requires the knowledge of the reaction macro kinetics. It can be determined separately in suitable small scale batch experiments as shown. Experiments with a homogeneous model reaction in a tubular pilot plant validate the theoretical method. (C) 2003 Elsevier Science B.V. All rights reserved.