We describe the development, numerical quantification, and application of a new class of microelectrochemical reactors (MECR). The reactors were fabricated using standard photolithographic techniques and a photosensitive propriety glass to yield structurally well-defined rectangular ducts of the following critical dimensions: height 25-100 mum, width 100-500 mum, and length 1-10 cm. Separate microelectrode sensors were constructed on a base plate, and the two components were bonded to yield the MECR. Finite element (FE) simulations were carried out to aid in the design and quantification of the voltammetric analysis performed using the new devices. The numerical results revealed the 3D fluid dynamic and mass transport behavior within these cells and were used to quantify the variation of the 3D current density at the working electrode as a function of the transport rate through the cell. Experimental MECR studies were undertaken using aqueous and organic solutions containing ferrocene and potassium ferrocyanide to establish the experimental variation of the electrolysis current as a function of the solution flow rate. In both the numerical and experimental cases, a well-defined relationship between the mass-transport-limited current and volume flow rate was observed, and quantitative agreement between theory experiment was obtained for all cases explored.