XFluid logo You can use this small and simple freeware program to calculate compositions of C-O-H fluid at pressures from 1 bar to 100 kbar and temperatures from 400°C to 2300°C for many samples at once, according to:

Zhang, C., Duan, Z.H., 2009. A model for C–O–H fluid in the Earth’s mantle // Geochimica et Cosmochimica Acta, V. 73, pp. 2089–2102.

 It is a wrapper for the C-O-H EOS library COHDLL.dll, used by the Excel program GFluid.xls of Chi Zhang and Zhenhao Duan, that can be downloaded from http://gcmodel.kl-edi.ac.cn/archives/programs.htm:

Zhang, C., Duan, Z.H., 2010. GFluid: An Excel spreadsheet for investigating C–O–H fluid composition under high temperatures and pressures // Computers & Geosciences, V. 36, No 4, pp. 569-572.

 The program can also estimate fluid compositions according to an old model of S.K. Simakov and L.P. Nikitina ("SN95" option instead "ZD10"):

Simakov, S.K., Nikitina, L.P., 1995. Connection of diamonds' occurence in mantle xenoliths and the upper mantle redox conditions // Geokhimia, No 2, pp. 163-173 (in Russian: Svyaz' almazonosnosti mantiynikh ksenolitov s okislitel'no-vosstanovitel'nimi usloviyami verkhney mantii).

 Implementation of this model is slightly modified: approximated Graphite-Diamond curve follows the EOS proposed in:

Fried L.E., Howard W.M., 2000. Explicit Gibbs free energy equation of state applied to the carbon phase diagram // Physical Review B: Condensed Matter, V. 61, pp. 8734–8743.

accepted in the model of C. Zhang and Z.H. Duan:

P,kbar = 14.47 + 0.0233 * T,°C + 1.09134e-6 * T,°C 2 - 1.1491e-10 * T,°C 3

 The model SN95 may have only historical interest; ZD10 is highly recommended.

 Tables calculated in XFluid can be loaded to TriQuick for plotting data on diagrams:

XFluid and TriQuick