In the past years the awareness on climate change, air pollution, and fossil fuel availability has been growing, which has pushed the automotive industry to search for new combustion systems as well as for the optimization of the current ones. In this respect, the gasoline engine has much potential for improvement especially in regard to fuel consumption. GDi engines are the natural upgrade of PFI gasoline engines and their use is expected to grow over the years. This paper explores the use of rate of injection (ROI) and rate of momentum (ROM) to characterize the internal flow of an ECN gasoline injector. Rate of momentum has been successfully used in Diesel injectors with this objective and for the first time, the measurements have been made on a GDi injector. The paper focuses on the experimental setup used and the different uncertainties and difficulties to translate the typically measured Diesel techniques to a gasoline injector; it presents the measurements obtained for rate of injection and for the different methodologies used for rate of momentum. The paper also contains internal flow simulations performed with CONVERGE to compare the results with those gathered experimentally; the comparison between the computational simulations and the experimental data resulted in good agreement.