The molecular exchange is a frontline technology in the process of gas recovery from natural gas hydrate deposits. In such a case, the caged methane (CH4) molecules are exchanged with carbon dioxide (CO2). The process efficiency depends on several factors, including pressure (p) and temperature (T) of the injected gas. There are quite a few conflicting views on the guest-guest exchangeability; mainly, it is unclear if the process is by molecular diffusion or by the reformation of hydrates. This study reports the replacement of CO2 by CH4 in primeval CO2 hydrates, below ice-melting temperature. Intuitively such a process is least preferred because CO2- hydrates are thermodynamically more stable than CH4- hydrates. We varied the injected gas (CH4) pressure in the range of 0.7–8.5 MPa. The co-existence of Raman signatures specific to caged CO2 & CH4 molecules supports the molecular replacement in virgin CO2 hydrates. Further, the diffusion of CH4 in both 51262 & 512 cages of sI hydrates offers a path for the mixed hydrate formation. Subsequently, the hydrate dissociation pattern also supports the rapid growth of mixed hydrates.