For tests on nonuniform oil shale retorting, Western Research Institute's 10-ton retort was loaded with shale rubble in zones of different permeability. The permeability of any given zone was determined by the particle size range loaded into that zone. The retort was studied using gas tracer techniques and flow model simulations. Results of these tracer studies are discussed in this report. Nine retorting and tracer runs were made on the retort. For each run, tracer injections were made into the main air flow inlet and into taps near the top of the retort. Detection taps were located at four levels in the retort with five taps on each level in tests S71 through S78 and six taps on each level in run S79. The oil shale rubble bed was configured with a cylindrical core in tests S71 through S78 and with two side-by-side regions with differing bed properties in test S79. Relationships are shown between the tracer response and sweep efficiency, oil yield, and local yield. Model simulations are compared with tracer responses and indicate fair agreement between model-estimated and measured response times but poor agreement on the shapes of the response curves. Although the data are scattered, there is suggestive evidence that the sweep efficiency of a retort can be determined using simple inlet-to-outlet tracer tests. Oil yield can also be predicted for the operating conditions used for the nonuniform retorting tests. More tests on retorts with intermediate degrees of nonuniformity must be made to confirm the correlations developed in this study. 15 refs., 9 figs.