This article describes a one-to-one comparison of spray performance for a single-fluid high-pressure swirl injection system (PSA) and a dual-fluid, air-assisted injection system (AAA) based oil high-resolution CCD images and phase Doppler anemometer measurements. Both atomizer concepts are used in direct-injection spark-ignition (DISI) engine applications, and the present experiments were carried out using original engine hardware. Spray characterization was obtained in constant-volume chambers at ambient conditions corresponding to typical injection windows in DISI engines. The temporal and spatial evolution of spray pattern, mean droplet size, and droplet velocity were considered as important parameters. At atmospheric gas conditions, the rate of axial penetration was similar for both sprays, but a fourfold increase in gas density resulted ill a reduction of similar to 50% and similar to 25% for the AAA and PSA, respectively. A higher level of droplet arithmetic mean diameter (D-10) was generally observed for both sprays at elevated gas densities, and a correlation factor was introduced to link the space-averaged D10 and the ambient gas density.