A new tomographic process measures the spatial phase fractions in slug flow and possesses high positional and temporal resolution. The measuring method is based on the electrical conductivity of the flowing fluids, which is measured between numerous parallel wires. The individual measurements are directly proportional to the relative liquid content. With the aid of an iterative reconstruction procedure they permit calculation of the phase fractions. The quality of reconstruction is improved by consideration of a priori knowledge. The temporal resolution is 0.009 s and the spatial resolution less than 0.1% of the flow cross-section.