The Mediterranean Outflow Water (MOW) spills from the Mediterranean Sea (east North Atlantic basin) west off the Strait of Gibraltar. As MOW outflows, it entrains eastern North Atlantic Central Waters (ENACW) and Intermediate Waters to form the neutrally buoyant Mediterranean Water (MW) that can be traced over the entire North Atlantic basin. Its high salinity content influences the thermohaline properties of the intermediate-deep water column in the North Atlantic and its dynamics. Here, the composition of MW in its source region (the Gulf of Cadiz, west off Strait of Gibraltar) is investigated on the basis of an optimum multiparameter analysis. The results obtained indicate that mixing of MOW (34.1% +/- 0.3%) occurs mainly with overlying ENACW (57.1% +/- 0.8%) in a process broadly known as central water entrainment. A diluted form (80% of dilution) of the Antarctic Intermediate Water (AAIW) reaches the region and also takes part in MW formation (8.3% +/- 0.5%). Finally, the underlying Labrador Sea Water (LSW) also contributes (0.4% +/- 0.1%) to the characteristics of MW. From these results and considering 0.74 Sverdrups (Sv; 1 Sv equivalent to 10(6) m(3) s(-1)) as the mean outflow of MOW, the MW exportation rate was inferred (2.2 Sv), which, decomposing MW, means that the MOW outflow is accompanied by 1.24 Sv of entrained ENACW, 0.18 Sv of AAIW, and <0.01 Sv of LSW.