The interest of oil industry in increasing heavy oil production has promoted the use of enhanced oil recovery techniques such as CO2 injection, which produce a decrease of oil viscosity and displacement of heavy oil from reservoir to surface. The design of these processes requires accurate data of densities, viscosities or surface tensions of (CO2 + hydrocarbon) mixtures in order to simulate the behaviour of these mixtures in the reservoir. An automated Anton Paar DMA HPM vibrating-tube densimeter was used to measure densities of this kind of mixtures, and a new mixture injection system, by means of two syringe pumps, was developed for the densimeter. The equipment operates at high pressure, which is controlled through a back pressure valve and a variable volume cylinder with a stepper motor. The estimated standard uncertainty of the density is +/- 0.9 kg m(-3) at temperatures below 373.15 K and pressure range (0.1-140) MPa. In this paper, the densities of the mixtures (CO2 + n-decane), (CO2 + n-dodecane) and (CO2 +squalane) are reported at T = (283.15-393.15) K and p = (10-100) MPa. (C) 2016 Elsevier B.V. All rights reserved.