The interaction forces between micron-sized bitumen (heavy crude oil) droplets in an aqueous medium were determined with colloidal particle scattering, a method based on calculating colloidal forces from droplet-droplet collision trajectories. The results indicate that, in addition to an electrostatic force, a heterogeneous protrusion structure on bitumen surface further increases the repulsive force. This structure was found to contain "bumps" of 50-100 nm in horizontal diameter and of 0-20 nm or more in thickness. The protrusion structure helps in stabilizing the emulsion at salt (KCI) concentrations up to 0.1 M. but fails to prevent droplet coalescence at 1 M KCl. This nonuniform structure was not found in the previous study using a surface force apparatus.