A lateral flow reactor (LFR) is a low pressure drop fixed bed reactor especially suitable for end-of-pipe treatment, for example, the Shell DeNO(x) system for selective catalytic reduction of NOx. Inherently, an LFR is prone to flow maldistribution, which in turn may negatively affect conversion. A detailed study of the hydrodynamics and overall reactor performance of an LFR is presented. The characterization of the flow patterns is carried out in detail with a 2D computational fluid dynamics (CFD) model. In addition, a "double 1D" hydrodynamic model is developed and validated against the CFD results. This computationally much more efficient model is extended with catalytic reaction kinetics, accounting for intraparticle mass transfer limitations. LFR efficiency can be defined as the ratio of the amount of catalyst needed in a fixed bed with uniform distribution over the amount of catalyst needed in the LFR to reach the same overall conversion. Despite the inherently limited flow uniformity, this efficiency of the LFR remains higher than 95% as long as the flow uniformity is above 50%, that is, for nearly all practical cases.