Ion-pair complexes of decavanadate were prepared with different cationic phase-transfer catalysts (PTCs) and their catalytic behavior was investigated in the oxidations of tetralin and cyclohexene with molecular O-2. It was found that both the PTCs themselves and their ion-pair complexes enhanced the rate of oxidation. The catalytic activities of both the PTCs and their ion-pair complexes depend strongly on their concentrations. At low concentrations (< 10(-3) M), the PTCs themselves (in the form of spherical inverse micelles) proved to be the more active but at higher concentrations where the growing micelles are transformed into a more open layer structure, the ion-pair complexes exerted the higher catalytic activities. At concentrations near 0.1 M the efficiencies of both types of catalysts decreased because the layers start to transform into a more closed micellar structure. The structure of the micelles is also influenced by the pH of the aqueous phase used during the preparation of the catalyst solutions.