Particle image velocimetry and FLUENT 6 computational fluid dynamics software were used to investigate single- and two-phase flow issuing from a coaxial air-blast atomizer. For a single-phase gaseous jet flowing through an annulus, the centerline velocity decays at a rate that is similar to a gaseous jet issuing from a circular orifice, beyond about 10 diameters downstream, and dimensionless axial velocity profiles are self-similar and in good agreement with the gaseous jet. In the case of a two-phase jet generated by an air-blast atomizer with mass loading between 0.2 and 0.35, the dispersed phase centerline velocity increases rapidly due to interaction with the annular gas flow and then decays at a rate that is slightly slower than a gaseous jet. The dispersed phase axial velocity profiles also compare well with that of a gaseous jet. Dispersed phase velocities determined using an Eulerian-Eulerian numerical model agree to within 10% of the experimental data about one diameter downstream.