The Microwave Sounding Unit (MSU) Ocean Precipitation product (MSUOP) provides gridded upper tropospheric temperatures derived from MSU instruments on several different platforms. The precipitation estimates follow the method of Spencer (1993). Oceanic precipitation is estimated by increased warming in MSU channel 1 over a threshold. The increased warming is attributable to emission by liquid water in the lower troposphere. MSU channels 2 and 3 are used to remove warming due to air mass differences. The MSU instruments measure the thermal emission of radiation by molecular oxygen at four frequencies near 60 GHz.