MacFlinCor was developed to process laboratory data gathered on fluid inclusions and to calculate P-T isochores for geologically important fluids composed of H2O, CO2, CH4, NaCl, and N2. Within the program, interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically. The user can choose from among multiple published equations of state describing fluid behavior and can easily compare the results obtained by using different equations. A case study of an Archean lode-gold deposit serves to highlight the operation of the program and the deciphering of the P-V-T-X-t conditions of multiple fluids in a complex paleohydrothermal system.