A special arrangement for ISS signal detection has enabled the sequential analysis by SIMS and ISS to be performed with SIMS apparatus. Using a mixed ion beam of He + and Ar + ions, the He + ions provide ISS signals while the Ar + ions generate secondary ions as usual. We have applied this approach to oxygen-enhanced secondary ion generation. ISS monitors the surface coverage of oxygen on a Ni sample and SIMS the generation of secondary ions, Ni + ions, for different partial pressures of oxygen in the specimen chamber. The present SIMS-ISS analysis has led to the conclusion that the electron tunneling model describes the experimental results with considerable success.