Shake flask experiments were conducted to determine the biodegradability of aqueous linear alkylbenzene sulfonate (LAS) and LAS (1600 mg dm(-3)) subjected to wet air oxidation (WAO), to assess the suitability of WAO as a pre-treatment for biological degradation. The effects of WAO temperature (180-240degreesC) and the concentration of the orthophosphoric acid catalyst (0-1.0 mol dm(-3)) were investigated. Results showed that a higher WAO temperature increased the biodegradability of the WAO effluent. This was due to a greater removal of both recalcitrant sulfonated organics and organic concentration (TOC and COD). Conversely, greater orthophosphoric acid concentrations decreased the biodegradability of the WAO effluents. This was because the higher acid concentration increased the ionic strength and changed the WAO intermediate and product distribution, inhibiting microbial action. Nevertheless, the effluents from both variations of WAO were still more biodegradable than LAS at equivalent concentrations. However, since higher WAO temperatures can substantially increase capital costs, future work should focus on developing a WAO catalyst that both desulfonates and mildly oxidises LAS at moderate temperatures (200degreesC).