Cone angles of sprays formed by a high injection pressure effervescent atomizer were investigated as part of a study concerning the application of effervescent atomization to diesel fuel injection. Spray cone angles were studied in high ambient density environments that simulate conditions inside the combustion chamber of a diesel engine at the end of compression. Cone half-angle is reported for different injection pressures (12.6-36.5 MPa; all pressures reported in this work are absolute), atomizing gas-to-liquid ratios by mass (GLR - 0.8-13.6%) and ambient pressures (0.27-5.5 MPa). Results show that cone half-angle lies between 5.8 and 11.5 degrees over the entire range of independent parameters studied, and increases linearly with increasing injection pressure or GLR at all ambient pressures. A more interesting result is that the cone angle first decreases when the ambient pressure increases from 0.27 to 1.5 MPa, but then increases as ambient pressure rises from 1.5 to 5.5 MPa. This is thought to occur because the two-phase flow leaving the injector is under-expanded at low ambient pressures. The following correlation for cone angle is developed from the measured data: alpha /2 = (0.15GLR) + (0.039P(inj)) + (0.0451P(amb)(4) - 0.6211P(amb)(3) + 2.7551P(amb)(2) - 3.62P(amb)) + 7.0. (C) 2001 Elsevier Science Ltd. All rights reserved.