Abstract: The main goal of this paper is to demonstrate the theoretical and practical use of dimensional analysis, π -theorem, to formulate a physical model of fluid flow from a reservoir. Such models are essential in chemical, mechanical, and reservoir engineering, specially, to find the time required to empty a tank or a reservoir. This work showed that dimensional analysis reduced the number of experimental variables to be correlated (measured), and pointed out the best experimental approach to the problem. Use of dimensional analysis results in significant saving of time, efforts and expense in experimental investigation and correlation.