Mössbauer spectra acquired by the Mars Exploration Rovers (MERs) often have low statistics with overlapped component spectra, making it difficult to fit individual spectra for all hyperfine or other parameters. When a set of spectra is complementary in the sense that components are weak in one and strong in another, analyzing the spectra simultaneously (simfitting them) while equating or relating parameters among the spectra will reduce parameter correlations and can lead to convergence of otherwise unfittable spectra. We apply an author-written Windows-based Mössbauer data fitting program to three cases from the MER data set to demonstrate the capabilities and advantages of the simfit method.