Vapor-phase OH-stretching overtone spectra of methanesulfonic acid and trifluoromethanesulfonic acid were recorded in the Delta v(OH) = 4 and 5 regions using cavity ring-down spectroscopy. We compare these spectra to those of sulfuric acid to consider the effect on vibrational overtone spectra of replacing one of the OH groups with a more or less electronegative group. We complement our experimental work with anharmonic oscillator local mode calculations of the OH-stretching frequencies and intensities. The presence of a weak intramolecular interaction between the hydrogen atom of the OH group and the oxygen atom of the adjacent SO group in methanesulfonic acid lowers its OH-stretching frequency from what would otherwise be predicted based on the electronegativity of the methyl group.