Before analysing the lubrication in a ring pack, first of all, it is necessary to determine the inter-ring gas pressures. They are the boundary pressures of the lubricating oil film on the sliding surface of the piston ring i. e. the pressures above, below and behind the ring. In the articles published recently on the ring pack lubrication, the gas pressure is calculated without considering the change of temperature. But the results of measurement show that the temperature of cylinder wall varies considerably in some operating conditions. In this paper, the authors not only take the change of gas mass but also the change of temperature into account. Calculation examples indicate that it is necessary to take the change of the temperature into account.