Transport experiments across polymer inclusion membranes (PIMs) are presented. The physical immobilization of trioctylamine (TOA) or methyltrioctylammonium chloride (TOMACl) as the ion carriers and o-nitrophenyl octyl ether as the plasticizer in cellulose triacetate as the support were used to prepare polymer inclusion membranes. The competitive transport of ReO₄^- ions from nitrate aqueous solutions through a PIM with TOA or TOMACl was investigated. The effect of the pH of the source aqueous phase on ReO4- transport from nitrate solution was studied. The higher efficiency of ReO₄^- removal was observed with use of the basic carrier. TOMACl. The selectivity of competitive oxoanions transport from the source phase decreases as follows: ReO₄^- > NO₃^- > SO₄^2-. This order of permeability correlates well with the energy of transported anions hydration.