We next calculated the gas working capacity (i.e., difference between uptake at low and high pressure, see Sec. 2) of the mechanically stable USMOF DB MOFs using GCMC simulations for both CO2 and CH4 (Supporting Information Figure ). We observe a number of MOFs in USMOF DB that have a CO2:CH4 working capacity ratio approaching 0.268 (Figure ). Notably, this number is the ratio of the standard CO2 working pressure (i.e., 16 bar -0.15 bar = 15.85 bar) to the CH4 standard working pressure (i.e., 65 bar -5.8 bar = 59.2 bar). These MOFs with CO2:CH4 ratio of approximately 0.268 have large pore volumes where gas molecules can reside without interactions with the framework, leading to gas uptake directly proportional to the ratio in pressure differences, with small deviations (i.e., an offset of 100 cm 3 (STP)/g framework obtained from fitting) from this behavior due to π-π stacking interactions between the CO2 molecule and the MOF pore walls 101 . This trend is even more evident in USMOF DB MOFs prior to applying the high mechanical stability (i.e., KVRH > 5 GPa) criterion because MOFs with extremely large pores often have poor mechanical stabilities and are thus excluded. The average and distribution of CO2 working capacities are similar for all three configurations of node and edges (average for 1inor-1edge: 414.19, 1inor-1org-1edge: 438.13, and 2inor-1edge: 414.81 cm 3 (STP)/g framework, Supporting Information Figure ). However, the 1inor-1org-1edge configuration has a higher average CH4 working capacity (670.01 cm 3 (STP)/g framework) compared to 1inor-1edge and 2inor-1edge configurations (513.47 and 529.33 cm 3 (STP)/g framework). This dependence of working capacities on the building block configurations can be understood in the context of geometric factors that differ between CH4 and CO2 (see discussion in Sec. 3c). In particular, MOFs with 1inor-1org-1edge configuration have 50% greater average gravimetric pore volume (4.70 cm 3 /g) compared to the other configurations (3.04 cm 3 /g for 1inor-1edge and 3.05 cm 3 /g for 2inor-1edge configuration).