In a year-long pilot experiment to the southwest of the Hawaiian Islands, we recorded teleseismic intermediate-period Rayleigh waves on ocean-bottom L-CHEAPO instruments using differential pressure gauges as sensors. We analyzed over 70 events and obtained accurate phase velocity estimates at periods between 15 and 70s. The average seismic structure beneath the pilot array does not deviate significantly from a standard seismic model of 100 Myr old oceanic lithosphere. However, we find strong lateral velocity variations across the array with large negative anomalies appearing within roughly 300km of the island chain. We are able to image the edge of the Hawaiian Swell and hence demonstrate the importance of making phase velocity measurements on the ocean floor. ¿ 1999 American Geophysical Union