Two different cobaltites, LaCoO3 and La0.5Sr0.5CoO3-delta, have been prepared and characterized by means of high energy Co K-edge and low energy O K-edge X-ray absorption spectroscopy (XAS). Even though half of the La(III) is substituted by Sr(II), little or no changes call be detected in the formal oxidation state of cobalt atoms. The presence of strontium cations induces two main effects in the chemical and electronic state of the perovskite. The charge balance with Sr(II) species is reached by the formation of oxygen vacancies throughout the network, which explains the well-known increase in the reactivity of this Substituted perovskite. O K-edge XAS experiments show that the Sr(II) species induce the transitions of d electrons of cobalt cations from low to high Spill Configuration. We propose that this change in Spill Multiplicity is induced by two cooperative effects: the oxygen vacancies. creating five coordinated cobalt atoms, and the bigger size of Sr(II) cations, aligning the Co-O-Co atoms, and favoring the overlapping of pi-symmetry cobalt and oxygen orbitals, reducing the splitting energy of e(g) and t(2g) levels.