The flow of oil containing admixtures of mineralized water droplets and meeting the counter flowing fresh water droplets of larger radius in the working zone of the mixing chamber of a jet hydraulic mixer is investigated. A mathematical model of coalescence of the mineralized and fresh water droplets has been developed. Based on empirical data, estimates of the hydrodynamic parameters of such a flow have been performed. Assumptions are made that mineralized and fresh water droplets are spherical particles, whose coagulation (coalescence) takes place when the trajectory of the mineralized water droplet crosses the fresh water droplet boundary. Calculation results are presented illustrating the influence of the radius and velocity of a fresh water droplet and also of oil velocity on the process of coalescence of these droplets.