High-pressure densities of ethane, pentane, pentane-d12, 25.5 wt % ethane in pentane-d12, 2.4 wt % deuterated poly(ethylene-co-butene) (PEB) in ethane, 5.3 wt % hydrogenated PEB in pentane, 5.1 wt % hydrogenated PEB in pentane-d12, and 4.9 wt % hydrogenated PEB in pentane-d12+23.1 wt % ethane

Densities at 30-150 degrees C and pressures to 3000 bar are reported for ethane, n-pentane, n-pentane-d(12), n-pentane-d(12) + 25.5 wt % ethane, and mixtures of poly(ethylene co-butene) (PEB) in ethane, and FEB in n-pentane, in n-pentane-d(12), and in an n-pentane-d(12) + 23.1 wt % ethane mixture. The density data are measured with a high-pressure variable volume cell adapted with a linear-variable differential transducer. A detailed comparison is performed for the experimentally measured densities obtained in this work to experimental data available in the literature and to correlations reported in the literature for n-pentane. The experimental densities reported in this work have an estimated experimental uncertainty of 1.0-1.5%.