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Implementation of Pure Fluid and Natural Gas Standards: Reference Fluid Thermodynamic and Transport Properties Database (REFPROP)


Major improvements have been made to the REFPROP program that impact how users incorporate new standards into their applications. A high impact standard, the GERG-2004 equation of state for natural gas mixtures, is now a key component of the REFPROP program.


Version 9.0 of the REFPROP software has been released. This new update adds many new standards that either have been recently adopted, or are in the process of becoming standards. Most notably are the AGA-8 and GERG-2004 equations for natural gas. AGA-8 has been the current standard for natural gas properties since 1992 but was not available in previous versions of REFPROP since it was only valid in the gas phase. This standard did not have the ability to calculate phase equilibrium properties, including dew points and bubble points. Although properties at the dew point were within the limits of the AGA-8 equation, the unknown equilibrium point became a real hindrance for natural gas processors. The GERG-2004 equation set out to overcome this deficiency and to add properties in the liquid phase and critical region. It was designed to be more accurate than the AGA-8 equation in the gas phase, so that it could become a new standard for the gas industry. This equation is currently being adopted by ISO, and other organizations will accept the ISO approval once it is available. The new equation dramatically improves the representation of not only natural gas properties, but properties of mixtures for other components as well that are cryogenic or contain carbon dioxide. The model is set up simply so that additional compounds can be included in the mixture by adding interaction parameters for systems with limited data. For those systems with extensive data, the excess Helmholtz energy portions of the mixture model can be incorporated as well with one additional parameter that determines the extent of the excess portion that is added.

Many other changes have been incorporated into the new version of REFPROP. New equations of state have been added for 33 fluids and new transport equations have been added for 15 fluids. All of these equations represent either fluid representations with lower uncertainties or new equations for important fluids that were not available previously. Some of these fluids include acetone, carbon monoxide, ethane, hydrogen, hydrogen sulfide, krypton, nitrous oxide, propane, sulfur dioxide, toluene, and xenon. Fluids with new transport equations include methane, octane, nonane, decane, R125, hydrogen sulfide, methanol, and ethanol. Work is in progress to add surrogate mixture models for aviation fuels and rocket propellants, models for biofuels, and updated transport surfaces for hydrogen to future versions of the REFPROP program.

Additional Technical Details:

Associated Publications:

Leachman, J.W., Jacobsen, R.T, Lemmon, E.W., and Penoncello, S.G., "Fundamental Equations of State for Parahydrogen, Normal Hydrogen, and Orthohydrogen," submitted to J. Phys. Chem. Ref. Data, 2008.

Lemmon, E.W., McLinden, M.O., and Wagner, W., "Thermodynamic Properties of Propane. IV. A Reference Equation of State for Temperatures from the Melting Line to 650 K and Pressures up to 1000 MPa," to be Submitted to J. Chem. Eng. Data, 2008.

McLinden, M.O., "Thermodynamic Properties of Propane. I. P-Rho-T Behavior from 265 to 500 K with Pressures to 36 MPa," Submitted to J. Chem. Eng. Data, 2008.

Ott, L.S., Huber, M.L., and Bruno, T. J., ”Density and Velocity of Sound Measurements on Five Fatty Acid Methyl Esters at 83 kPa and Temperatures from (278.15 to 338.15) K”, J. Chem. Eng.Data, 53, 2412–2416 (2008).

Huber, M. L., Lemmon, E.W., Kazakov, A., Ott, L.S., and Bruno, T.J., ”Model for Thermodynamic Properties of a Biodiesel Fuel”, work in progress, for submission to Energy & Fuels

Huber, M.L., Lemmon, E.W., Diky, V. , Smith, B.L., and Bruno, T. J., ”Chemically Authentic Surrogate Mixture Model for the Thermophysical Properties of a Coal-Derived-Liquid Fuel”, Energy & Fuels,22,3249–3257(2008).

Huber, M.L., Smith, B.L., Ott, L. S., and Bruno, T. J., “A Surrogate Mixture Model for the Thermophysical Properties of Synthetic Aviation Fuel S-8”, Energy & Fuels,22,1104-1114(2008).

Huber, M.L., Lemmon, E.W., Ott, L. S., and Bruno, T. J., ”Surrogate Mixture Models for the Thermophysical Properties of Rocket Propellants RP-1 and RP-2”, work in progress, for submission to Energy & Fuels

Major Accomplishments:

  • Released of version 9.0 of REFPROP
  • Incorporated the AGA-8 and GERG-2004 models for natural gas
  • Incorporated new wide-ranging surface for the viscosity of methane
  • New equations of state have been added for 33 fluids
  • New transport equations for 15 fluids
REFPROP Database Images
Collage of REFPROP Database Images

End Date:


Lead Organizational Unit:



Customers:  The REFPROP program is in use in nearly every country in the world and in many key corporations requiring fluid properties in the U.S. Up to 1000 copies of the program are sold each year, some of which incorporate the software into their applications and then distribute the modified package to their customers.

Collaborators:  Ruhr University, Bochum, Germany


Eric W. Lemmon
Marcia Huber
Mark O. McLinden


General Information:
Eric Lemmon
303-497-7939 Telephone

325 Broadway
Mailcode 838.08
Boulder, CO 80305-3337