Six isoniirogenous (31% crude protein), isocaloric (3.7 kcal g-1 ME), practical diets with variable levels of carbohydrates (starch) and lipids (soybean oil) were formulated to determine the ability of Oreochromis niloticus fmgerlings to utilize each nutrients as an energy source. The diets were fed to triplicate groups of fish at a daily rate of 5% of body weight for 16 weeks. There were significant differences in the growth and feed conversion of Nile tilapia fed diets with carbohydrate-to-lipid (CHO : L) ratios ranging from 4.8 to 1.22. A diet containing CHO : L ratio of 4.8 :1 showed significantly lower performance, persumably due to low fat content in the diet. These results indicate that Nile tilapia can efficiently utilize carbohydrate and lipids as an energy source. They can be substituted for one another at a rate of 2.89:1, commensurate with the CHO:L physiological fuel values.