The oil-in-water emulsion is increasing in popularity as a cost-reducing method for "heavy" crude oil transportation. In order to analyze the effect of oil-in-water ratio and emulsifier amount on the viscosity of the final emulsion, concentrated model-emulsion of oil-in-water were rheologically characterized. Two emulsification methods were investigated: batch and "in-flow" in a lab scale plant. Comparison revealed the effect of the emulsifier amount both on the viscosity decay during time and on the final emulsion viscosity. Qualitative microscopy results revealed a rather wide drop size distribution for systems exhibiting a lower viscosity value.