In this communication, the experimental parameters and sorption isotherms of CO2 on moisture-equilibrated Argonne premium coal samples provided by Goodman et al. [Goodman, A.L., Busch, A., Bustin, R.M., Chikatamarla, L., Day, S., Duffy, G.J., Fitzgerald, J.E., Gasem, K.A.M., Gensterblum, Y., Hartman, C., Jing, C., Kross, B.M., Mohammed, S., Pratt, T., Robinson Jr., R.L., Romanov, V., Sakurovs, R., Schroeder, K., White.. C.M., 2007. Inter-laboratory comparison II: CO2 isotherms measured on moisture-equilibrated Argonne premium coals at 55 degrees C and up to 15 MPa. International Journal of Coal Geology 72, 153-164] were used to investigate the reasons that CO2 Sorption on coal diverged significantly among the laboratories at high pressure. We demonstrate that the experimental parameters for manometric equipment affect the CO2 isotherms at high pressure. High adsorption values may be obtained with a higher volume in the reference cell or a lower void volume in the sample cell. Although the impact of experimental parameters for manometric equipment on CO2 Sorption on coals is not clear, the investigation of the equation of the Gibbs excess adsorption used to obtain incremental adsorption shows that higher sorption of CO2 can be obtained with a higher ratio of the volume of the reference cell to the void volume of the sample cell for manometric equipment. On the other hand, higher adsorption is difficult to obtain at high pressure with a smaller volume ratio. (C) 2007 Elsevier B.V. All rights reserved.