When an electrode reacts with a chemical species in a fluid, a current is generated that can be measured to determine the amount of the reactant in the fluid. For sufficiently small electrodes, the measuring process is, to good approximation, insensitive to fluid motion, as the microelectrode is housed within a nearly stagnant layer of fluid. In this work we elucidate the effect of convection on the response of a microsensor electrode. The transient convective-diffusion equation that describes mass transport of the chemical species to the electrode contains a single dimensionless group, the Peclet number, and solutions are found on a three-dimensional domain using a modified version of oblate spheroidal coordinates.