We have used nuclear magnetic resonance relaxometry to study emulsions of viscous crude oils for water concentrations in the range 4.9-50.1 wt.%. We obtained the dependences of the proton relaxation parameters for the components of the emulsions (water in droplets, hydrocarbon medium, and boundary phase) on their treatment parameters and the water concentration. The experimental results are interpreted within a proposed model for the proton dynamics. We establish experimental relations between the NMR relaxation parameters and the integral diameters of the water droplets, characterizing their size distribution, for emulsions of crude oils, residual oils, and bitumens.