Global surface pressure data from 1976 to 1997 from over 7500 land stations and the Comprehensive Ocean–Atmosphere Data Set have been analyzed using harmonic and zonal harmonic methods. It is found that the diurnal pressure oscillation (S1) is comparable to the semidiurnal pressure oscillation (S2) in magnitude over much of the globe except for the low-latitude open oceans, where S2 is about twice as strong as S1. Over many land areas, such as the western United States, the Tibetan Plateau, and eastern Africa, S1 is even stronger than S2. This is in contrast to the conventional notion that S2 predominates over much of the globe. The highest amplitudes (∼1.3 mb) of S1 are found over northern South America and eastern Africa close to the equator. Here S1 is also strong (∼1.1 mb) over high terrain such as the Rockies and the Tibetan Plateau. The largest amplitudes of S2 (∼1.0–1.3 mb) are in the Tropics over South America, the eastern and western Pacific, and the Indian Ocean. Here S1 peaks around 06... Abstract Global surface pressure data from 1976 to 1997 from over 7500 land stations and the Comprehensive Ocean–Atmosphere Data Set have been analyzed using harmonic and zonal harmonic methods. It is found that the diurnal pressure oscillation (S1) is comparable to the semidiurnal pressure oscillation (S2) in magnitude over much of the globe except for the low-latitude open oceans, where S2 is about twice as strong as S1. Over many land areas, such as the western United States, the Tibetan Plateau, and eastern Africa, S1 is even stronger than S2. This is in contrast to the conventional notion that S2 predominates over much of the globe. The highest amplitudes (∼1.3 mb) of S1 are found over northern South America and eastern Africa close to the equator. Here S1 is also strong (∼1.1 mb) over high terrain such as the Rockies and the Tibetan Plateau. The largest amplitudes of S2 (∼1.0–1.3 mb) are in the Tropics over South America, the eastern and western Pacific, and the Indian Ocean. Here S1 peaks around 06...