The balance spreadsheet method is applied to mass analysis of the Environmental Control and Life Support System (ECLSS). This method is used to analyze the requirements for ECLSS carbon dioxide, latent water, crew potable water, crew hygiene water, crew hygiene waste water, crew urinal water, crew waste water, animal potable water, animal hygiene water, hydrogen, oxygen, nitrogen, and various solid wastes. The spreadsheet layout reduces the complexity of the ECLSS analysis by concisely defining the sources, sinks, and net changes in mass for each fluid. This approach also builds the data base by assigning an area for time-independent data and another one for time-dependent data so that layout modifications and formula implementations can be easily accomplished. The analysis method is illustrated by using information from the latest Space Station ECLSS Architectural Control Documents and a given Space Station assembly sequence. The analysis results are plotted and discussed.