Semibatch wet air oxidation (WAO) experiments were conducted on aqueous solutions of linear alkylbenzene sulfonates (LAS) at various pH's, to determine whether acidic and/or. basic pH affects the rate and extent of the degradation and desulfonation of LAS and its refractory sulfonated intermediates. It was found that acidic pH increases the removal of TOC, COD, and LAS, as well as increasing desulfonation. Acid catalysis of the desulfonation and aromatic ring cleavage reactions is thought to be responsible. Conversely, the WAO of LAS and its intermediates was less effective at high pH. It is hypothesised that this is due to radical scavengers and the dominance of the superoxide radical in the alkaline environment. Desulfonation might also be autocatalyzed in unmodified LAS WAO reactions by reaction products, as acid is a product of LAS WAO reactions. Experiments were conducted at 240 degreesC at neutral (unmodified) and alkaline pH's to compare WAO in the presence and "absence" of this acid. Desulfonation occurred to the same extent at both pH's, indicating that it was not significantly autocatalyzed by the acid generated during WAO.