In measurement science many diverse densimeters are used to measure the density of gas mixtures and the accuracy of such measurements can be significantly influenced by adsorption of gas-mixture components on the internal surfaces of the densimeter. In this context, the major objective of the present study was to investigate the influence of adsorption and desorption on the accurate density measurement of gas mixtures. For this purpose, measurements of the p-rho-T-x behavior of a 15-component natural-gas mixture were carried out as an example. The densities were measured at T = 273.15 K with pressures up to 8 MPa (which was at least T = 25 K above the maximum dew-point temperature) using an accurate two-sinker densimeter incorporating a magnetic suspension coupling. Densities at standard conditions (T = 273.15 K, p(o) = 0.101325 MPa) were also measured utilizing a special two-sinker densimeter without magnetic suspension coupling. For both instruments, the relative expanded combined uncertainty (k = 2) in density was 0.02%. The measurement results are illustrated in diagrams demonstrating the consequence of sorption effects, which is a change of the gas density inside the measuring cell resulting from a change in composition of the measured gas. Due to these sorption effects significant errors in density measurement can occur, up to about 0.1% in case of the typical example investigated within the present study. To avoid a distortion of the measurements by sorption effects, appropriate measurement procedures were undertaken. (C) 2014 Elsevier Ltd. All rights reserved.