Today 90% of electricity in the world is produced from fossil fuels such as coal, oil and naturel gas. Oil equivalent of fossil in the world is calculated to be 68% coal, 18% oil and 14% natural gas. According to these figures the lifetime of oil, natural gas and coal is 40, 60 and 220 years respectively. Coal water slurries (CWS) and coal oil mixtures (COM) may be an alternative energy source to fuel-oil. In COM or CWS technology, the coal loading rate is an important factor and it depends on the rheology of mixtures. In this study, the COM was prepared using fuel-oil(#6) and high rank bituminous coal at a temperature range 20 to 90°C and coal loading rate were examined. The results of the study showed that the rheology of COMs loaded with high amount of coal as much as 60% could be advanced by increasing the mixture temperature to 90°C. However, for slurries with suitable viscosity, the mixture temperature at 60°C is found to be enough with lower coal loading rates such as 50%. In conclusion, it was found that fuel-oil can be loaded with high amount of solids using high rank coals. Thus, the consumption rate of fuel-oil could be decreased without sacrificing on the heating value of the new fuel, COM.