The characteristics of the two-phase flow and the spray formed in an effervescent atomizer were experimentally investigated over a range of flow rates, gas-to-liquid ratios (GLR), injection pressures, and discharge orifice diameters. The Reynolds number (Re), defined with the orifice diameter as the characteristic length, was seen to be a pertinent parameter in addition to GLR for determining the transition from the bubbly flow to slug flow. The discharge coefficient of the atomizer in the bubbly flow regime and the Sauter mean diameter of the spray in the annular flow regime were found to scale with the parameter (GLR (Re)0.5). The structure of the spray and the measured values of cone angle of the spray showed distinctly different features in the bubbly, slug, and annular flow regimes. A two-dimensional simulation of the flow and spray structure reproduced the gross features observed in the experiments. © 2009 Begell House, Inc.