A quadratic-speed-dependent Voigt line shape (qSDV) with line mixing (qSDV+LM), together with spectroscopic line parameters from Devi et al. [1,2] for the 2v 3 band of CH 4 , was used to retrieve total columns of CH 4 from atmospheric solar absorption spectra. The qSDV line shape [3] with line mixing [4] was implemented into the forward model of GFIT (the retrieval algorithm that is at the heart of the GGG software [5]) to calculate CH 4 absorption coefficients. High-resolution laboratory spectra of CH 4 were used to assess absorption coefficients calculated using a Voigt line shape and spectroscopic parameters from the atm line list [6]. The same laboratory spectra were used to test absorption coefficients calculated using the qSDV+LM line shape with spectroscopic line parameters from Devi et al.[1,2] for the 2v 3 band of CH 4 and a Voigt line shape for lines that don't belong to the 2v 3 band. The spectral line list for lines that don't belong to the 2v 3 band is an amalgamation of multiple spectral line lists. We found that for the P, Q, and R branches of the 2v 3 band, the qSDV+LM simulated the laboratory spectra better than the Voigt line shape. The qSDV+LM was also used in the spectral fitting of highresolution solar absorption spectra from four ground-based remote sensing sites and compared to spectra fitted with a Voigt line shape. The average root mean square (RMS) residual for 131,124 solar