The paper describes detailed studies about the spray formation of a direct-injection high-pressure gasoline injector and the interaction of the droplets with the surrounding compressed air in pressure chamber experiments and inside an optically accessible research engine. Different optical techniques, like stroboscopic video technique, high-speed filming with flood-light illumination or with light-sheet illumination by a copper vapour laser, particle image velocimetry of the droplets, laser-induced fluorescence of the liquid phase, and spontaneous Raman spectroscopy for the measurement of the fuel/air ratio are used. From the recorded images spray characteristics such as spray penetration and spray cone angle are evaluated for different settings of the chamber pressure and temperature and for different rail pressures. The results show that all techniques are suitable to derive the quantities mentioned above. Their differences are not larger than the shot-to-shot variations, but for a direct comparison of results it is advisable to keep the same optical technique.Measurements performed in the combustion chamber of a DI gasoline engine show stronger cycle-to-cycle variations compared to pressure chamber experiments. Both systematic pressure chamber experiments under well defined conditions as well as measurements in optically accessible engines highlight special phenomena of the spray formation process and thus support the development of the combustion process for DI gasoline engines.