The present study focused on the effervescent atomization of oil-in-water emulsions to evaluate the influence of viscosity ratio and initial oil drop size on the oil drop size after atomization. Constant atomization conditions were assured by spray drop size measurements. The viscosity ratio of the emulsion was varied between 0.24 and 27 by changing the oil viscosity. The initial oil drop size was adjusted to values from 0.67 to 21 mu m. The disperse phase content was set to 1 wt-% to exclude coalescence phenomenon of the oil drops. The low disperse phase content was also chosen to ensure comparable process conditions especially the stresses acting on the oil drops in atomization. Oil drop breakup was visible for atomized emulsions with initial oil drop size above 2 mu m, while oil drops in the emulsion with an initial oil Sauter mean diameter of 0.67 mu m remained stable in effervescent atomization. In terms of viscosity ratio, oil drop breakup was found up to a viscosity ratio of 13.5. Comparing oil drop breakup results to those of capillary rheology measurements with defined shear rates we conclude that the shear rates acting on the oil drops in the effervescent atomizer were higher than 1.000.000 s(-1). (C) 2016 Elsevier B.V. All rights reserved.