Type I antimonide diode lasers operate in the 2000 to 2800 nm spectral region. Compared to the 1300 to 1650nm communications spectral band, the antimonide band can access stronger molecular transitions and thus potentially achieve higher sensitivity. Compared to quantum cascade or lead-salt lasers operating at longer infrared wavelengths,antimonide lasers have the advantage that both laser and detector technology support room temperature, cw operation. This paper describes experiments to measure ammonia and methane simultaneously, with high sensitivity and fast response, using a distributed feedback laser at 2200 nm. Our approach is based on scanning the laser over a small spectral regionthat encompasses several lines, either by varying the laser temperature or current, while simultaneously using wavelength modulation with harmonic detection to record the spectrum. Temperature scanning is slower but can cover a wider spectral interval. Digital signal processing methods, including classical least squares and singular value decomposition, extract the gas concentrations from the measured spectra. The accuracy and precision of these algorithms are compared in two limits: the limit when both gases are absent or present only at low levels, and the limit when the concentration of one gas is high.