The seepage of gas through coal and in particular through coal briquettes has already been a quite well known phenomenon. This also refers to its influence on certain initial conditions of coal and gas outbursts such as threshold values of so called gas stresses. In turn a detailed research on the influence of sorption processes on these conditions has been neglected until now. There is, however, an opinion that ( fast) desorption is crucial for rock and gas outburst initiation and continuance, although many examples contradict such a thesis. The goal of the studies described here was to investigate a part of this ambiguity, namely the influence of sorption processes on gas stresses leading to coal and gas outbursts carried out in laboratory conditions. A series of laboratory experiments concerning provoking coal and gas outbursts was conducted. Coal briquettes and two gases: nitrogen and carbon dioxide were used. The experimental data was computed out into the gas stresses and the most important information was extracted. The obtained results showed that in experiments with nitrogen slightly higher gas stresses and thus more intensive provoking were needed in order to initiate outburst than in experiments with carbon dioxide. It indicates that sorption may be the factor that promotes outbursts. Comparative analysis implied also that for a given level of gas stresses the more sorptive the gas was, the longer it took to initiate an outburst. Moreover, in the experiments with nitrogen the global maximum of gas stresses occurred deeper inside of the briquette for any given time than in experiments with carbon dioxide. All the found differences were weak, though easily noticeable. (C) 2010 Elsevier Ltd. All rights reserved.