Waves in the neutral upper atmosphere have been measured by the open source neutral mass spectrometer (Oss) during both the elliptical and the circular phases of the Atmosphere Explorer-C mission. Typical peak-to-peak wave amplitudes seen in [N2] are 30%, although amplitudes of 55% have been recorded. The amplitudes are mass dependent, Ar showing the largest perturbation. Helium is typically found to be out of phase with the heavier constituents. A survey of Oss data from 338 circular orbits shows that the highest wave amplitudes and the greatest number of occurrences are found in both the northern and the southern high-latitude regions. The near-simultaneous measurements of waves in both hemispheres at high latitudes also point toward a source related to conjugate phenomena. A possible second class of lower-amplitude waves peaks at high latitudes; however, a secondary peak near ±25° magnetic latitude may be due to waves generated near the equatorial region. A study of wave amplitudes and occurrences during a magnetic storm shows a possible transpolar propagation of waves from a magnetically active region near local midnight. The assumption of horizontal propagation would explain the observed high-latitude distribution of large-amplitude waves. The results of this study are compared with previous measurements of neutral wave structure.