The hydrofluoroolefin 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf) is a refrigerant with a low global warming potential that can be used as a working fluid in refrigeration cycles, heat pumps, and organic Rankine cycles (ORC). This paper aims to accurately describe the thermodynamic properties of HFO-1234yf with the molecular based BACKONE equation of state (EOS). The BACKONE parameters are fitted to experimental vapour pressures and saturated liquid densities. For the ideal gas heat capacities very recent experimental results are taken. For the data used in the fit, the uncertainties of calculated values from the BACKONE EOS are 0.36% for vapour pressures and 0.37% for saturated liquid densities. For predicted data, the uncertainties of calculated values from the BACKONE EOS are 0.29% for liquid densities and 0.99% for pressures in the gas phase. Predicted isobaric heat capacities in the liquid are within the experimental uncertainties of +/-5%. Comparisons with the results from the extended corresponding state (ECS) model and with recent molecular simulation data confirm the high quality of the BACKONE EOS. (C) 2011 Elsevier B.V. All rights reserved.