Generation of volatile fatty acids (VFAs) during anaerobic diges­tion of sludge have higher commercial value than methane produced subsequently. Therefore, it was decided to study conditions, e.g. pH and temperature, necessary to maximize production of VIA, concentrations of individual fatty acids were measured. Total volatile fatty acids production of the treated sewage sludge was increased with the depth of the acid phase reactor. In a reactor of 100 cm depth and 30 cm width, volatile fatty acids increased from 37.1 meq/L at the first port (15 cm from top) to 78.8 meq/L at the fourth port (center of the reactor 60 cm from top). Moving toward bottom or top of the reactor decreased total fatty acids content, and then de­creased to reach 45.8 meq/L at the seventh port (lower port). Studying the volatile fatty acid fractions using gas chromatography techniques showed that the volatile fatty acids fractions were acetic, propionic, iso­buteric, buteric and caproic acids. The quantity of the volatile fatty acid fractions concentration followed the aforementioned sequence. The highest content of the volatile fatty acids fractions were recorded in the samples withdrawn from port No. 4 (middle of the reactor), while the lowest quantities recorded toward the top and the bottom of the reac­tor. Favorable pH values were around 6 and below 7.