The FITDAT Utility is written as a FORTRAN subroutine that is called from a driver routine, and is part of the Ansys Chemkin library. We provide both C++ and FORTRAN driver routines. The driver routine performs the function of allocating total memory usage through definition of array sizes, as well as opening input and output files. FITDAT checks internally to ensure that the allocated work arrays are sufficiently large to process the input data. Users modifying the programs should be experienced with compiling and linking program files on their operating system and must have either a C++ or FORTRAN compiler installed.