This article examines the development of water-swellable rubbers for oil and gas production packer equipment. The object of the investigation is to document the effect of rubber's acrylonitrile content on the swelling of the elastomers modified with sodium-carboxymethyl cellulose and a copolymer of acrylamide and potassium acrylate. After testing the samples at room temperature, the most influential factor in a material's swelling was discovered to be the mineral content in the liquids imitating well fluids. NBR polarity stemming from the inherent CN-group level was not explicitly detected to affect the swelling rate and maximum ratio under the described conditions of the experiment. It was determined that in sodium chloride aqueous solutions with concentrations from 3 to 22%, swelling of nitrile rubber mostly depends on its cross-linking degree.