Samples of PrBaCo2O5.50+delta (delta = -0.15-0.14), synthesized by solid-state reactions, were investigated to ascertain oxygen compositional effects on transport/magnetic properties. Resistivity decreases with increasing oxygen content, indicative of p-type conduction. A metal-insulator transition was observed at 330 K only for sample PrBaCo2O5.52, coinciding with phase transition and spin-state transition of Co3+. When delta deviates from zero, samples show insulator-insulator transitions, although for sample delta = 0.14, no transition occurs but only semi-conductive behavior appears. Electronic transport is governed by the hopping mechanism at lower temperatures and thermal activation at higher temperatures. All samples underwent paramagnetic-ferromagnetic-antiferromagnetic transitions, except PrBaCo2O5.64, which only went through a paramagnetic-ferromagnetic transition. The ferromagnetic state for delta < 0 originates with the Co3+/Co2+ super-exchange interaction; for delta>0, it stems from the Co3+/Ce4+ double exchange interaction. (C) 2015 Elsevier Ltd. All rights reserved.