Large storage tanks may require mixing to achieve homogeneity of contents for several reasons : prior to sampling for mass balance purposes, for blending in reagents, for suspending settled solids for removal, or for use as a feed tank to a process. At Oak Ridge National Laboratory, mixed waste evaporator concentrates are stored in similar to 190-m(3) (50000-gal) horizontal tanks, about 3.7 m (12 ft) in diameter and 18 m (60 ft) in length. This tank configuration has the advantage of permitting transport by truck and therefore fabrication in the shop rather than in the field. A survey of the literature revealed no information on mixing large storage tanks with length-to-diameter ratios greater than 2. Jet mixing experiments were carried out in two model tanks : a 0.87-m(3) (230-gal) Plexiglas tank that was similar to 1/6 linear scale of the actual waste tanks and a 95-m(3) (25000-gal) tank that was about 2/3 linear scale of the actual waste tanks. Mixing times were measured by the use of a sodium chloride tracer and several conductivity probes distributed throughout the tanks. Several jet sizes and configurations were tested. In the 0.87-m(3) tank, jet diameters of 0.016, 0.022, and 0.041 m (0.62, 0.87, and 1.61 in.) were used. In the 95-m(3) tank, jet diameters of 0.035 and 0.049 m (1.38 and 1.93 in.) were used. One-directional and two-directional jets were tested in both tanks. Mixing times for each tank were correlated with the jet Reynolds number and for the two tank sizes using the recirculation time for the developed jet.