We present a study of the correlation between gamma ray emission (E<100MeV) from the Perseus molecular cloud complex measured with the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) and HI, 12CO & 13CO observations from the DRAO 26m antenna and the AT&T Bell Labs. 7m telescope, respectively, towards the Perseus Molecular Cloud Complex. The radio maps cover roughly 10-square degrees and have been convolved to the resolution of the EGRET instrument of 30'x30'. A comparison between the results for 12CO and 13CO is made with respect to the use of 12CO as a tracer of column density. We find that both can be, equally well, fit to the gamma ray data. Determination of whether 12CO or 13CO provides a better fit, or whether 12CO suffers from opacity effects is limited by the statistics of the gamma ray data.