Dispersion of femtosecond laser pulses propagating in Ar, He, Kr, ${\mathrm{N}}_2$ , Ne, Xe, and their mixtures is measured by spectrally and spatially resolved interferometry. By varying the gas pressure in a $4.5\mathrm{m}$ long tube between $0.05\mathrm{mbar}$ and ambient pressure, the first, second, and third order phase derivatives of broadband laser pulses are determined at $800\mathrm{nm}$ under standard conditions. The dispersion of gases and gas mixtures obeys the Lorentz–Lorenz formula with an accuracy of 0.7%. Based on the measured pressure dependent dispersion values in the near infrared and the refractive indices available from the literature for the ultraviolet and visible, a pressure dependent Sellmeier-type formula is fitted for each gas. These common form, two-term dispersion equations provide an accuracy between $4.1\times {10}^{-9}$ (Ne) and $4.3\times {10}^{-7}$ (Xe) for the refractive indices, from UV to near IR.