The semibatch wet air oxidation (WAO) of 1600 mg L-1 of a linear alkylbenzene sulfonate (LAS) known as sodium dodecylbenzene sulfonate (SDBS) was investigated, for varying oxidation temperature from 180 to 240 degreesC and pressure from 3.05 to 6.55 MPa. The major reaction products identified were low-molecular-weight volatile fatty acids (VFAs) such as formic and acetic acids, sulfonated aromatics, and sulfate. For 120-min WAO at 1.5 MPa oxygen partial pressure, a temperature increase from 180 to 240 degreesC led to increases in the liquid-phase LAS removal from 79 to 100%, in the COD removal from 23 to 70%, and in the desulfonation of the LAS molecule from 7.4 to 57% of the total theoretical sulfate. Increasing the overall oxidation pressure from 3.05 to 6.55 MPa had little effect on the overall TOC and COD degradation, but increased the desulfonation. On the basis of these results, a reaction mechanism is proposed. Sulfonated aromatic WAO intermediates accumulated under the conditions used, indicating that, to achieve further organic degradation, more effective desulfonation conditions will be required.