A semi-industrial scale test was conducted to thermally treat mixtures of spent oil and askarels at a concentration of 50,000 ppm and 100,000 ppm of polychlorinated biphenyls (PCBs) under a reductive atmosphere. In average, the dry-basis composition of the synthesis gas (syngas) obtained from the gasification process was: hydrogen 46%, CO 34%, CO 2 18%, and CH 4 0.8%. PCBs, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans (PCDDs/PCDFs) in the gas stream were analyzed by high-resolution gas chromatography (GC)-mass spectrometry. The coplanar PCBs congeners 77, 105, 118, 156/ 157, and 167 were detected in the syngas at concentrations Ͻ2 ϫ 10 Ϫ7 mg/m 3 (at 298 K, 1 atm, dry basis, 7% O 2 ). The chlorine released in the destruction of the PCBs was transformed to hydrogen chloride and separated from the gas by an alkaline wet scrubber. The concentration of PCBs in the water leaving the scrubber was below the detection limit of 0.002 mg/L, whereas the destruction and removal efficiency was Ͼ99.9999% for both tests conducted. The concentration of PCDDs/PCDFs in the syngas were 8.1 ϫ 10 Ϫ6 ng-toxic equivalent (TEQ)/m 3 and 7