Free-energy landscapes of chemical reactions are expressed in terms of reaction coordinates, similarly barriers of "breathing" MOFs in the osmotic ensemble appear at specific cell volumes. In the case of methane adsorption in DUT-49, such a barrier is associated with a sharp transition between op and cp phases with large changes in volume. In the present work, we employed molecular simulations to treat the cell volume (V ) as a "reaction coordinate" in the osmotic ensemble. The osmotic potential as a function of volume reveals the (meta)stable states of interest, and the barriers between them, for any set of thermodynamic parameters µ, p and T . With this method, detailed landscapes of the osmotic potential, as a function of cell volume of DUT-49 and methane gas pressure, have been computed at 90 K, 120 K and 150 K. This complete thermodynamic analysis provides unprecedented insight into the phase stability under adsorption. The produced osmotic potential surface can recreate experimental observations, demonstrating the effects of temperature and outlining the stable and metastable phases present during NGA, paving the way for understanding other complex adsorption processes.