A comparison is made between plasma profiling time-of-flight mass spectrometry (PP-TOFMS) and nuclear reaction analysis (NRA) for depth profiling of 18O tracer in porous anodic oxide films on aluminum. The films were formed galvanostatically, for a range of times, using phosphoric acid electrolytes that were either enriched in 18O or of the natural isotopic concentration. The morphologies of the films were determined by electron microscopy. The findings from PP-TOFMS and NRA reveal a partitioning of the tracer between the surface regions and buried layers of the films. However, a relatively high background of 16O in PP-TOFMS prevents a reliable quantification of the concentration of 18O.