The goal of this study is to analyze the effects of changes of blood flow in penetrating arterioles (PAs) on the spatial distribution of tissue oxygen levels in the cerebral cortex. A theoretical model is used to simulate blood flow and oxygen transport in the cortical microcirculation. Networks containing up to 20,000 vessel segments, covering regions up to 1.1 mm, are generated by combining multiple hexagonal units, each fed by one PA. Varying numbers of adjacent PAs are constricted to 50 % of their original diameters, resulting in PA flow reduction by 93 %. With constriction of one or two PAs, the predicted minimum oxygen partial pressure is in the range 10-20 mmHg, corresponding to mild hypoxia. When three or more adjacent PAs are constricted, severe hypoxia (partial pressure below 10 mmHg) is predicted. Thus, oxygenation of the cortex is predicted to be only mildly affected by flow reduction in isolated PAs, but vulnerable to flow reduction in multiple adjacent PAs. Further simulations are used to explore the effects of flow redistribution while holding overall perfusion constant. If one PA is constricted and one adjacent PA is dilated, mild hypoxia is present. With three PAs constricted and four adjacent PAs dilated, regions of both mild and severe hypoxia are predicted. These results show that redistribution of blood flow, caused for instance by disruption of mechanisms for local blood flow regulation, can result in tissue hypoxia, even in the absence of reduced perfusion.