Well-width dependence of quantum and transport mobilities of electrons in GaAs/GaAlAs multiple quantum wells is studied for wells with widths ranging between 50 Angstrom and 145 Angstrom. Experimental results are obtained from the amplitude analysis of the Shubnikov-de Haas (SdH) oscillations and from conventional Hall measurements at temperatures between T = 15 K and 4.2 K. A novel technique is employed to estimate, theoretically, the interface roughness parameters from electron quantum and transport lifetimes. The modelling is carried out for a range of layer fluctuations, width (Delta) and lateral size (Lambda), as to obtain the best fit to the experimental results for individual samples. Our results indicate that the interface roughness scattering limits equal both quantum and transport mobilities at low temperatures, and that the nature of scattering by interface roughness (small or large angle) depends not only on the size and the width of the fluctuations but also on the distribution of these fluctuations within the samples. Therefore, unlike the predictions of the existing theoretical models, which assume constant values of Delta and Lambda for all well widths, the well-width dependence of interface roughness scattering cannot be verified experimentally. (C) 1997 Academic Press Limited.