The effects of alkyl chain length and concentration of surfactant on the yield stress-pH behavior of a 57 wt% ZrO2 suspension were evaluated, An alkyl chain length n of between 5 to 12 carbons was used, For chain length n greater than or equal to 7, a much larger maximum yield stress (at zero zeta potential) than that without additive was recorded. The increase in the maximum yield stress is as much as sixfold, Generally, a higher surfactant concentration leads to a higher yield stress, The increase in the maximum yield stress is quite insensitive to surfactant chain length, Ionic strength appears to have no effect on the yield stress-pH behavior of suspensions with a surfactant, The data are consistent with the observation of a long-range attractive (hydrophobic) force measured. in surface force experiments.