A few number of gas reservoir parameters regulate the intensity and the extent of gas emissions during and following the mining of coal. Gas content is one of the most important of these parameters. Depending on the purpose of its quantification its accurate determination could be vital to the mining activities. For instance, if this parameter is used to evaluate the outburst and its value falls near the threshold limit it needs to be accurately measured. Similarly when seam gas emissions from coal mines, is to be calculated, an accurate measurement of this parameter in a carbon constraint economy has a very important economic impact. The other challenge associated with gas content is the lower limit of measurability of the standard systems. For instance for low to very low gas content (<0.1 m3/t) encountered in ‘non-gassy’ underground and open cuts, the standard method is unable to deliver accurate values. A different methodology is then required to evaluate the gas content in these conditions. Another parameter, important in evaluation of the intensity of the emissions and its time dependency nature is the gas diffusivity parameter. While the saturation indicates the onset of gas desorption, the diffusivity parameter controls the rapidity of gas movement from the micro storage sites into the larger fractures and voids. Diffusivity is, therefore, the primary rate limiting factor in the intensity of gas emissions. The diffusivity is not often measured directly and a diffusion time constant, called Tau, is often used to indicate the speed of diffusion flow in coal. This parameter is also used in numerical simulators which use a simplified model of gas diffusion, namely pseudo state diffusion models. This paper discusses the current and new methodologies to determine the main parameters of coal reservoirs including gas content and gas diffusivity and potential errors associated with current measurement methods.