Accurate density measurements on three binary (hydrogen + argon) mixtures were carried out at temperatures between 273.15 and 323.15 K and at pressures up to 9 MPa, utilizing a two-sinker magnetic suspension densimeter. The measurements resulted in a total of 144 (p, rho, T, x) data points. The gravimetrically prepared mixtures contain a hydrogen mole fraction of 0.06078, 0.29892, and 0.55073. When taking the measurement uncertainties in temperature, pressure, density, and composition into account, the combined expanded uncertainty (k = 2) was estimated to be less than or equal to 1.16 x 10(-3) rho. Relative deviations of the measured densities from values calculated with the GERG-2008 equation of state were within 0.44% for the composition with a hydrogen mole fraction of 0.06078, up to 1.17% for the composition with a hydrogen mole fraction of 0.29892, and up to 1.01% for the composition with a hydrogen mole fraction of 0.55073.