With the advent of modern bioengineering tools, photosynthetic organisms are increasingly being engineered to produce chemicals from CO2 sources, thereby creating a potential route of sustainable chemical production. Cyanobacteria have evolved a carbon-concentrating mechanism (CCM) that enables growth at low-environmental carbon concentrations. However at high-carbon concentrations these benefits may not outweigh synthesis costs. Here, mass transport and kinetic modeling analyses were performed on two species of cyanobacteria as well as a hypothetical no-CCM mutant. Modeling results correlated with published experimental data. Three conclusions were drawn from the analysis. Carboxysome geometry was unimportant due to the fast relative rate of diffusion of carbon species. Interspecies variations were largely due to active HCO3- transporters. The no-carboxysome cell approaches the wild-type at 10% CO2. Therefore, in high CO2 environments the carboxysome and active bicarbonate transporters provide no benefit and a metabolic advantage could be achieved by eliminating the energy-intensive CCM proteins. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 1269-1277, 2014