This study investigates the production of spherical carbons from cellulose under sub- and supercritical ethanol conditions with and without the addition of a potassium hydroxide (KOH) catalyst. Different temperatures (200 and 280 A degrees C), residence times (0.5, 1, 2, and 4 h), and KOH concentrations (5, 10, and 20 wt% of cellulose) were used for the carbonization process. Carbon spheres could only be obtained under supercritical ethanol conditions (at 280 A degrees C and 9.5 MPa). Supercritical ethanol decreases the oxygen content by a significant amount, thereby increasing the heating value. Morphological studies show that the carbons are essentially spherical of different sizes depending on the operating conditions (such as the presence of a catalyst and time). For the first time, we showed that spherical carbons can be obtained under supercritical ethanol conditions. This is a useful result as, for instance, ethanol can be produced from cellulose, and this opens the possibility for the development of a green and simple procedure to synthesize carbon spheres that may have many different applications including gas separation, catalysis, and energy storage.