There is increasing evidence for a global trend towards lower seawater dissolved oxygen levels, which poses a threat to marine ecosystem health. A particular concern is upwelling areas, such as the Benguela Upwelling System, that is predisposed to low oxygen levels with occasional catastrophic consequences for fisheries resources. In the Southern Benguela Upwelling System, the lowest seawater O2 levels are typically found in inshore bottom waters at relatively shallow depths on the shelf. In order to better understand the factors inducing low oxygen conditions, temporal trends, and to provide input to the Department of Environmental Affairs' annual State of the Oceans and Coasts Report, oxygen data had been collected approximately 3-monthly along 4 transects, since 2014. To this dataset had been added data collected on a random sampling grid in the vicinity of the monitoring lines. The dissolved oxygen, temperature and salinity data represent stations at a maximum depth of about 500 m, for cruises conducted on the R/V Algoa in: August 2014 (AUG14), October 2014 (OCT14), February 2015 (FEB15), May 2015 (MAY15), September 2015 (SEP15), November 2015 (NOV15), February 2016 (FEB16), May 2016 (MAY16), August 2016 (AUG16), November 2016 (NOV16), February 2017 (FEB17) and May 2017 (MAY17).