The paper deals with the nonequilibrium poroelectroelastic theory (PEET) for polymer electrolytes (PE) under the conditions of water electrolysis with a view of further use in the theoretical description of mass transfer processes in layers of a membrane-electrode assembly. Moreover, this paper presents a review and analysis of the models of electrochemical and mass-transfer processes in electrolyzers, and analyzes problems associated with their physicochemical description. The authors came to the conclusion that it was necessary to use models of water sorption and PE swelling. It was further concluded that the existing PEET may be most suitable to be modified for use under nonequilibrium conditions during electrolysis. The fundamental equation for pressure balance of the classical equilibrium PEET for PE was considered. A modification of the PEET was carried out in order to use it under nonequilibrium conditions of water electrolysis for the purpose of further modeling of mass transfer processes. Based on experimental data available in open sources, the authors studied properties and features of the elastic forces in PEs, and then refined the dependencies of the elastic forces in PE on swelling and temperature. Taking into account the existing experimental data on the permeability of gases in a PE and the swelling property of a PE when in a contact with liquid water, parameters of the nonequilibrium PEET were obtained for the conditions of water electrolysis. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.