There remain discrepancies in the determination of the total and elastic cross sections for electron and positron collisions with carbon dioxide at impact energies from 0.3 to 100 eV. We have carried out a joint experimental and theoretical study in an attempt to resolve the differences. Our measurements for total cross sections for electron impact agree extremely well with those of Hoffman et al. [Phys. Rev. A 25, 1393 (1982)] above 2 eV, while those for positron impact agree to better than 15% in magnitude, and are in an excellent accord for the energy-dependence. The present observations, along with an analysis using a knowledge of the dominant inelastic processes, lead us to conclude that the total cross section determined in earlier studies is a considerable underestimate at intermediate energies, where inelastic processes are not negligible. The analysis provides a rationale for understanding the discrepancies. Furthermore, we present that the total cross section by positron impact below 2 eV becomes larger by 20% than that of electron impact, and provide a rationale as well as implication to a possible application. (C) 1997 American Institute of Physics. [S0021-9606(97)01841-2].