A Group for High Resolution Sea Surface Temperature (GHRSST) Level 4 sea surface temperature analysis produced daily by Ifremer/CERSAT (France) using optimal interpolation (OI) on a regional 0.02 degree grid. It provides a daily cloud-free field of foundation sea surface temperature at approximately 2 km resolution (0.02 degree) for the Mediterranean Sea. It is generated by merging microwave and infrared satellite sea surface temperature observations including those from the Advanced Very High Resolution Radiometer (AVHRR), the Advanced Along Track Scanning Radiometer (AATSR), the Spinning Enhanced Visible and Infrared Imager (SEVIRI), the Advanced Microwave Scanning Radiometer-EOS (AMSRE), and the Tropical Rainfall Measuring Mission Microwave Imager (TMI). The satellite SST observations are intercalibrated using the AATSR sensor as a reference (previously re-calibrated using all available in situ data). This dataset was the first Level 4 product produced by the GHRSST Project. It has been superseded by the ODYSSEA L4 product for this region: GHRSST Level 4 ODYSSEA Mediterranean Sea Regional Foundation Sea Surface Temperature Analysis.