In this work, a rolling ball viscometer was developed that makes it possible to measure viscosity, density, and phase equilibria simultaneously. The cell is mounted inside a high-pressure vessel and can be used at pressures up to 30 MPa and temperatures up to 200 degrees C. Calibration of the viscometer was carried out by using water at inclined angles from 10 to 30 at temperatures of 40 degrees C and 80 degrees C and at pressures up to 20 MPa with toluene viscosity being used for confirmation; viscosity measurements of toluene were found to agree with literature data to within 0.66% in average relative deviation. Viscosity, density, and bubble-point pressure of ethanol + CO2 systems were measured at 40 degrees C; bubble-point pressures for the ethanol + CO2 system agreed to within 2.2% of the literature. Viscosity of the ethanol + CO2 system were measured at saturated and pressurized liquid states and viscosity values decreased with increasing CO2 composition, and decreased to about half the value of pure ethanol for 0.32 mol fraction of CO2. (C) 2019 Elsevier B.V. All rights reserved.