Auger line shape, energy shifts, and profiling techniques have been used to analyze the anodic oxide/InP interface. The composition and bonding of oxides grown in either 0.1 N KOH or 3% tartaric acid/propylene glycol electrolytes were investigated. Plots of the P(KL2L2) and the In(M4,5N4,5N4,5) line shapes provided useful information in determining the boundaries between predominately In–O/In–P and P–O/P–In bonding. The oxides were determined to have an outer layer of a mixture of In and P oxides. The transition from In–O bonding to In–P bonding for the tartaric acid-grown oxide occurred over a greater thickness than for the KOH-grown oxide. The P–O to P–In bonding transition occurred over approximately the same thickness for both oxides.