This paper reports an investigation on the volume-based drop size distribution of sprays produced by swirl atomizers dedicated to direct-injection spark-ignited engines. Because of the use of high injection pressures to reduce the atomization time, the spatial density of the spray is high and prevents from classical measurements of spray drop size distribution. This problem is overcome by combining an experimental approach to the application of the maximum entropy formalism (M.E.F.). Based on the determination of correction factor series to correct the measurements from multiple light scattering, the experimental procedure allows obtaining some distribution characteristic features. According to a previous study, two of these characteristics are used as information in a M.E.F. procedure to derive the spray volume-based drop size distribution. This characteristic is of paramount importance for evaluating the large drop population with accuracy. The overall procedure is presented in detail and discussed. It was applied to a series of four swirl atomizers in order to study the influence of the nozzle geometry and of the injection pressure on the injector performances. Conducted under both stationary and transient working conditions, this study allows a more precise understanding of the performances of GDI injectors as far as the spray drop size distributions are concerned.