The advantage of the pyIAST package is that we obtain the optimal IAST prediction given the experimental (or computational) data that are provided, and we do not have to rely on a fitting step. However, this also implies that pyIAST is unable to extrapolate to pressures higher than are provided. pyIAST extrapolates beyond the last pressure point by assuming that saturation was reached, and the loading is a constant, equal to the largest loading available in the pure component data. The pyIAST gives a warning that it had to use extrapolated data, but it can not give an indication of the error this might give. This is best illustrated in the left-hand side of Figure .