An analysis is made of subsurface water masses in the subtropical western South Pacific Ocean, using temperature-salinity and temperature-oxygen relations. Seven major water masses, characterized by extreme values of salinity and oxygen, are distinguished. These are the Subtropical Lower Water (salinity maximum), the upper oxygen minimum, the Subantarctic Intermediate Water (oxygen maximum), the Antarctic Intermediate Water (salinity minimum and oxygen maximum), the deep oxygen minimum, the Deep Water (salinity maximum), and the Bottom Water. The core layer method is used to describe the distribution of the different water masses and to draw conclusions on their spreading.