This volume covers Leg 30 of the cruises of the Drilling Vessel Glomar Challenger. Leg 30 was the second cruise of D/V Glomar Challenger in the southwest Pacific arc and marginal sea complex. Previous drilling was carried out on Leg 21. The cruise commenced at Wellington, New Zealand on 24 April 1973 and ended on 13 June 1973 at Guam. During Leg 30 Glomar Challenger steamed 5273 nautical miles (9765 km) and drilling was carried out at five sites, although eight sites were planned for the leg. In view of the extremely complex geological history of the region, the problems that could be resolved in a single leg were very limited. The major general objectives of Leg 30 included: 1) Ages and their trends in marginal basins: South Fiji and Coral Sea; 2) Complete the biostratigraphic zonations for the equatorial Pacific; 3) Obtain further data on the oceanographic and tectonic history of the southwest and western equatorial Pacific; and 4) Structure of an oceanic plateau. Sites 285, 286, and 287 were directed toward the ages and history of marginal basins. Two sites were planned to investigate the Ontong-Java Plateau and its margins. Site 64 on the Ontong-Java Plateau penetrated 985 meters of middle Eocene to Recent biogenous sediments, bottoming in chert horizons. Two sites were planned to complete the biostratigraphic section below the chert (Site 289) and to investigate plateau structure and lithology of reflecting horizons below the chert horizons (Site 288).