Gas content can be considered the most important parameter for assessing emissions from coal seams during and post mining. Traditionally, the purpose of gas content determination was to assess gas outburst potentials and to quantify the magnitude of gas emissions into underground headings and at the coal face. Therefore, it’s a traditional definition; measurement and determination are based on these objectives. However, the calculation of emissions from mining for the purpose of establishing a greenhouse gas inventory would require new definitions for gas content and new measurement methods. Moreover, errors inherent in measuring gas content need to be quantified so that the uncertainty of emissions inventory can be evaluated. Therefore, various definitions of gas content in relation to the purpose of its use are suggested. Anew method of measurement for low gas content coals is discussed. Moreover, various parameters influencing the value of measured gas content are discussed and errors of estimation using the direct method are evaluated.