A mathematical model describing vertical sulfate gradients as a function of diffusion, bacterial reduction, and sedimentation is applied to calculate the steady‐state rates of sulfate reduction in coastal sediments. Diffusion coefficients of sulfate are determined experimentally in different sediment types and depths. The rate of sulfate reduction is also determined directly on sediment cores by a radiotracer technique. Experimentally determined rates are compared with those calculated from the model. The results of the model are shown to depend strongly on its assumptions about the kinetics of bacterial sulfate reduction.