Nine bands (0-0, 0-1, 0-2, 0-3, 1-2, 1-3, 1-4, 1-5 and 2-4) of the B2Σ+-X2Σ(+) system of the 13C16O+ molecule have been photographed under high resolution and their fully resolved spin-rotation structure has been observed at high J values. Only well-resolved lines for J > 17.5 were used in the analysis. Molecular constants obtained from individual least-squares fits for each band of the system were subject to a stepwise merge. Using these merged molecular constants the set of equilibrium molecular constants for the 13C16O+ molecule has been determined for the first time. © 1993 Academic Press, Inc.