We analyzed the formation rates of gas hydrates from methane/CO2 mixtures associated with contaminated well gas streams, which results in a methane-enriched gas product. The initial pressure affects both the final clean gas composition and the time taken to achieve it. Although promoters have been described, we note that this term often refers to interstitial materials that stabilize equilibrium hydrate structures rather than classical chemical rate promoters (i.e., catalysts). We also show that previously reported hydrate rate improvers are irrelevant for commercial purposes because they merely overcome inadequate mixing systems. We identify the key process requiring rate acceleration and show the potential for reducing the time for this process to make selective CO2 hydrate formation commercially attractive. We also examine the effect of salinity on the selective formation of CO2 hydrates. The phase boundary pressures increase with increasing salt concentration, and the rate of formation decreases. Formation times are on the order of 1 h, so catalysts are required to make this process commercially viable. © 2009 American Chemical Society.