A theoretical and experimental study of flow distribution and it's effect on converter performance is presented. Measurements of velocity distribution are presented for a series of canisters with varying cone angles and the degree of maldistribution associated with each design is reported. Pressure drops measured across monoliths are also reported. The results show reasonable agreement with values obtained from the Hagen-Poiseuille equation.Analytical data from aged catalysts are presented showing radial poison distribution. The effect of thermal gradients within the catalyst during engine aging is also studied. A limited study has shown that the latter effects predominate.The prediction of flow distribution in the canister is described. Two and three dimensional computational fluid dynamics models are used to simulate flow in the canisters. The predictions are used to compare with experimental results and to highlight differences between the two and three dimensional approach.A multi-channel, non-adiabatic, reaction model is incorporated within the three dimensional flow simulation. The presence of reaction under non-adiabatic conditions is predicted to marginally smooth flow distribution, however radial flow variations are predicted to have a significant effect on the conversion profile in the monolith.