The present work deals with the broadening of rotational lines of the carbon monoxide 2-0 band by both argon and hydrogen chloride. A high resolution grating spectrometer with a spectral slit width of 0.07 cm-1 was used, necessitating only a small correction in observed half-width values. Sufficiently small contributions of CO self-broadening were obtained by using long pathlength cells of 12 meters for CO-argon mixture and 1 meter for CO-HCl mixture. Half-width results, which are considered accurate to within ±5 percent, are presented in the form of a table and by a graph.