This is an experimental study of the effects of liquid viscosity (mu(L)) and surface tension (gamma) on the size of droplets produced by an atomizer fed with a two-phase gas/liquid (TPGL) mixture. The nozzle is a one-quarter scale model of an industrial fluid coker nozzle used for bitumen upgrading. The primary objective of this study was to compare the Sauter mean diameter (SMD or D(32) or D(qp)(q-p) = integral(Dmax)(Dmin) D(q) dn/dD dD/integral(Dmax)(Dmin) D(p) dn/dD dD) of the TPGL sprays for different mu(L) and gamma. Compressed air was used as the gas phase; the liquid phases were water, canola oil and a glycerine-water solution. The mu(L) was varied from 1 mPa s to 67 mPa s, and gamma was varied from 25 mN/m to 61 mN/m. The liquid flow rates were varied from 0.095 L/s to 0.105 L/s, and the gas-to-liquid ratio (GLR or beta = (m) over dot(g)/(m) over dot(l)), by mass, was fixed at 2%, similar to the ratio used in commercial fluid coker nozzles. Fluid mixing pressures in the test were between 400 kPa and 700 kPa. The D(32) within the spray was measured using a Dantec 2D-Fibre mode Phase-Doppler-Particle-Anemometer (PDPA). With measurements performed at axial distances of 100 and 202 mm from the nozzle orifice and within a spray radius of 40 mm. The results showed that the 67-fold increase in mu(L) results in 46 mu m increase in D(32) which roughly extrapolates to a power law relationship exponent of 0.11 (based on two points). In contrast, the 2.4-fold increase in gamma indicates roughly 42 mu m increase in D(32), giving an exponent of -0.24. For both parameters the exponent is small, indicating weak dependence. The gamma effects appear stronger, but the modest increase is barely exceeds the margin of error. (C) 2010 Elsevier Ltd. All rights reserved.