Three computer programs, PLUME, OUTPLM, and DKHPLM, have been used by the U.S. Environmental Protection Agency and municipalities to estimate initial dilutions of sewage discharged into marine environments. Modification of the input parameters for the three programs, while maintaining the appropriate gravitational direction and ambient density gradient, permitted the use of the programs to predict the centerline dilution, trapdepth, and maximum penetration of negatively buoyant fluids. Drilling fluids and other negatively buoyant fluids were discharged downward into a 4000-liter tank of stratified, static seawater to obtain verification data. Time-lapse photographs were taken through a window, and replicate synoptic samples were obtained through 3-7 sampling ports along the centerline of the fully developed plumes. Samples were analyzed gravimetrically for total solids and spectrophotometrically for soluble components. The conclusions were (1) all three computer program predictions were in good agreement with the measurements and observations made on a limited number of representative plumes generated in the hydraulic model, and (2) the solid and soluble components of the tested drilling fluids appeared to dilute at dissimilar rates within the buoyancy and momentum-dominated initial dilution phase.