Mass-transfer properties of a continuously reciprocating paddle reactor are investigated using computational fluid dynamic simulations. The flow induced by the paddle motion is modeled with a moving mesh assuming laminar flow. Spatial and temporal mass-transfer data are gathered over many paddle cycles under diffusion-limited conditions. Transient, numerical simulations of this type are computationally expensive, but can add insight into flow phenomena that are difficult to observe experimentally. It is shown that a major source of the agitation in a paddle cell is vortices shed from the paddle. This results in a mass-transfer limit that is periodic in nature and that may exhibit spatial variations related to the paddle wake. A simulation-based, mass-transfer correlation is presented that relates various design and operating parameters within a generic paddle reactor. The mass-transfer trends predicted by the numerical simulations are compared with experimental mass-transfer correlations found in the literature. © 2005 The Electrochemical Society. All rights reserved.