PURPOSE: To obtain the titled stable fuel oil having excellent combustion efficiency and effects on saving of fuel consumption and pollution control, by dispersing and emulsifying an aqueous solution containing specific anionic polysaccharides in heavy oil.

CONSTITUTION: One or more anionic polysaccharides selected from agar, carrageenan, glucomannan, guar gum, karaya gum, locust bean gum, tragacanth gum and xanthan gum in an amount of 0.0001W0.1wt.% are added to water to provide en aqueous solution and preferably Ca, Ba or Al cations, etc., in an amount of 0.0001W0.01wt.% are then preferably added. The above-mentioned aqueous solution is subsequently dispersed and emulsified in heavy oil, such as heavy oil A, B or C, heavy crude oil or regenerated heavy oil B, to produce an emulsified fuel oil containing preferably 60W85vol.% heavy oil and 15W40vol.% water. Furthermore, the size of waterdrops at this time is preferably about 10W20μm and homogenized.