Entrainment numbers (E) for conventional effervescent atomizer-produced sprays are reported Entrainment numbers were calculated using the expression of Ricou and Spalding [12]plus measured spray entrainment and momentum rate data determined during this study. Results showed that entrainment number increases with liquid viscosity, with atomizer exit orifice diameter, and with the combined effects of surface tension and liquid density. This is in contrast to results reported for ligament-controlled effervescent atomizer sprays [6], in which fluid physical properties had no significant effect. A possible cause for this discrepancy is the known unsteadiness of conventional effervescent sprays [11]. Dimensionally scaling entrainment numbers by liquid density and orifice diameter collapsed the majority of the data onto a single line. The modfied form for E describes the entrainment behavior of conventional effervescent sprays to within 25%.