Water-in-oil (W/O) emulsions are present in applications from well drilling to refining and cause diverse problems. The present paper details the results of a study of the stability and homogeneity of W/O emulsions of a heavy oil using the optical microscopy technique. The W/O emulsions used previously dehydrated heavy oil with the addition of increasing volumes of 10, 20, 30, 35 and 40% w/v of deionized water and formation water, under mechanical stirring at 2500, 5000, 10,000 and 15,000 rpm. Moreover, a saturated sodium chloride solution was added to the oil in the contents at 10, 20 and 30% w/v under stirring at 5000 rpm, in order to verify the influence of the electrolyte type on the stability of the emulsions. The W/O emulsions were subjected to a gravitational separation test to verify stability and photomicrographs of the emulsions were analyzed to evaluate the homogeneity and the droplet size distribution (DSD). The results showed that the prepared emulsions were stable and homogeneous even after aging for 30 days and after being subjected to heating. This stability may be related to the high content of resins and asphaltenes in the studied oil. The emulsions prepared with formation water showed higher DSD values than those prepared with saturated NaCl solution and deionized water. This distinction of droplet sizes can be related to the presence of ions of different charges in the formation water.