This talk will present our demonstration of wavelength modulation spectroscopy (WMS) of CO2 at pressures greater than 30 atm using a fast-scanning MEMS laser. Wavelength modulation spectroscopy is a fast, sensitive technique in which one varies the laser across an absorption feature of interest while applying a high frequency (f) modulation. The resulting harmonic signals, particularly at 2f, are sensitive to the absorbance of light by the molecules, which is a function of gas conditions such as temperature, pressure, and concentration. Traditionally, the technique has been limited to lasers with small tuning ranges; thus the use of a MEMs VCSEL with a large tuning range enables the measurement of high-pressure gases and large molecules that were difficult to measure before. Finally, a simulation of WMS is presented that accommodates the unique properties of the MEMs laser and will enable the extraction of the gas properties from the measurements made.