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The reaction of fenitrothion with a series of -nucleophile oximates having pKavalues in the range of 7.7−11.8 was studied both in the absence and presence of cetyltrimethylammonium (CTA) surfactants. Reaction with CTA−oximates was found to proceed through two pathways:  SN2(P) and SN2(C); an SNAr pathway was not observed. Accordingly, the observed rate constants were dissected into the two corresponding SN2(P) and SN2(C) pathways. Use of the pseudophase ion exchange (PPIE) model for micellar catalysis in the CTAsystem allowed evaluation of micellar second-order rate constant (k2m) parameters and binding constants, (KS). KSvalues for CTA−oximates were found to vary with the counterion, and the rate enhancement depended on a combination of KSand k2mvalues. k2m/k2wvalues ranged from 0.0025 to 0.64, suggesting that a concentration effect is mainly responsible for the rate enhancement. In the absence of surfactant, an -effect (i.e., k/knormal) varying from 8 to 450 was observed for the oximate reaction, decreasing with increasing pKa. It is proposed that differential solvation (transition-state imbalance) is a cause of the -effect in this system.