Data on drop size distributions formed during oil-water flows is presented in this paper; the data was obtained using a video recording technique which employed an endoscope. The experiments were performed with both the water and the oil (1.6 mPa s viscosity and 801 kg m(-3) density) as continuous phases, in two 1-in nominal bore horizontal test sections, made from stainless-steel and acrylic resin, respectively. Continuous phase velocities from 1.1 to 1.7 m/s and dispersed phase Volume fractions from 3.4 to 9% were used. The experimental drop size distributions were satisfactorily represented by the Rosin-Rammler distribution (Eq. (14)), with the values of the parameter delta ranging from 2.1 to 2.8. The results showed that the drop size distributions were strongly influenced by the pipe material, with the drops being smaller in the steel than in the acrylic pipe for the same flow conditions. They were also influenced by the nature and the velocity of the continuous phase. Both the maximum and the Sauter mean diameters were found to depend on the (-1.8) power of the continuous phase velocity. None of the theoretical correlations for the maximum drop size could represent accurately the experimental data, while the often used Hinze (1955) equation underpredicted the experimental results in all cases.