Today, the scenario of a well-controlled large-scale production of naroparticles is a very important aspect in nanotechnology. The present work aims at the investigation of different engineering aspects on the production of nanoparticles using microemulsions. A microemulsion made out of water, cyclohexane and surfactant is loaded with two reactants, BaC12 and K2SO4, to carry out a BaSO4 precipitation. A nonionic technical surfactant, Marlipal O13/40 is employed, as this surfactant is cheap and therefore preferred for an up-scale approach. The influence of suitable process control parameters like the feeding rate, the stirring rate, the feeding sequence or the initial concentrations of the reactants on the particle size has been studied to gain a deeper understanding of the important controlling mechanisms in the formation of nanoparticles in a non-ionic water/oil microemulsion. An extensive investigation of the microemulsion phase diagram was performed to find safe and convenient particle synthesis conditions. The particle precipitation was carried out in a semi-batch reactor. Transmission electron microscopy was used to analyze the size, the size distribution and shape of precipitated nanoparticles. A measurable influence on particle size was found for different initial concentration ratios of the two reactants. It was also found that with increasing particle size the shape changed from spherical to cubic. A corresponding Monte-Carlo simulation qualitatively confirms the observed changes in particles size. Theoretical arguments, based on the occupancy number, the critical nucleation number and the corresponding number of nucleated particles can be given to explain this change. (c) 2005 Elsevier Ltd. All rights reserved.