Gas adsorption at high pressures in porous solids is commonly quantified in terms of the excess amount adsorbed. Despite the wide spectrum of adsorbent morphologies available, the analysis of excess adsorption isotherms has mostly focused on microporous materials and the role of mesoporosity remains largely unexplored. Here, we present supercritical CO2 adsorption isotherms measured at $$T=308$$ T = 308 K in the pressure range $$p=0.02{-}21$$ p = 0.02 - 21 MPa on three adsorbents with distinct fractions of microporosity, $$\phi_2$$ ϕ 2 , namely a microporous metal-organic framework ( $$\phi_2=70$$ ϕ 2 = 70 %), a micro-mesoporous zeolite ( $$\phi_2=38$$ ϕ 2 = 38 %) and a mesoporous carbon ( $$\phi_2