The relationship between the geometric proportions of a simple external-mixing plain-jet airblast atomizer and the characteristics of the generated spray pattern has been investigated. The experimental conditions varied in the range of Re = 1236 to 3540, We = 65 to 595, and air/liquid velocity ratio 15 to 110. The minimum Sauter mean diameter was obtained when the axial location of the liquid orifice is such that the air jet impinges the liquid jet at 45 degrees and the exposure length is maximal. The Sauter mean diameter is found to be proportional to (V-f/V-a(3))(0.5) over the entire range of operational conditions (within an error of +/-7.5%). The most uniform droplet distribution was obtained when the axial location of the liquid orifice is such that the air jet impinges on the liquid jet at the orifice mouth with an impingement angle of 30 degrees.