Accurate optical emission spectroscopy (OES) measurements are necessary for plasma semiconductor processing and for optical emission analysis. In this paper we investigate the effects of self-absorption on the most important neutral Argon spectra lines. One of these Argon spectral lines (750 nm) is frequently used for actinometry. The experiment is performed in a reactive ion etch (RIE) capacitively coupled plasma (CCP) system. A comprehensive design of experiments has been created to establish all plasma conditions, power, pressure and gas flow rate which affect the Argon emission intensity by self-absorption. The results are then compared to theoretical calculated line ratios.