A project involved solidification/stabilization of a hydrocarbon sludge in a silty clay matrix cemented with a pozzolanic lime-fly ash admixture. The compactable mixture can harden as a dimensionally stable landfill monolith that minimizes contaminant mobility. The solidification/stabilization product has more than 50% porosity to contain the sludge in the available airspace. This limits the strength to that of a firm cohesive soil, and mass behavior is evaluated by traditional geotechnical methods. Customary influences on fine soil permeability apply as well, with compactive effort alone affecting results over a range from 10 to the-5 power to 10 to the-7 power cm/sec. The solidification/stabilization process retards hydrocarbon mobilization primarily by physical microencapsulation. Less than 5% of the carbon was mobilized in 10-pore volumes of throughput in column leaching tests. This solidification/stabilization method appears to be suitable to allow reuse of the surface for industrial purposes as long as cap integrity is maintained. Consequently, the potential use of cemented clay solidification/stabilization for hydrocarbon-contaminated soils in highway rights of way is also indicated.