Gas chromatography/mass spectrometry and ion chromatography were used to analyze the gases evolved from Ba1 - xKxBiO3 samples upon dissolution in normal and 18O-enriched aqueous acid solutions. The gases detected were O2, Cl2, and ClO2. In the superconducting range of x = 0.35 to 0.5, the solid oxide phases were a minor contributor to the total gas concentration, with more than 90% of the evolved gas being Cl2 formed by the the oxidation of the hydrochloric acid solution by Bi+5. The dependence of the Cl2, ClO2, and O2 evolution on the composition of the dissolved solid shows that the holes introduced by K substitution for Ba in BaBiO3 go onto Bi sites, increasing their oxidation state, rather than into the O band. © 1991.