Hydrological, ADCP, and drifting buoy data obtained during the GOGP99 Experiment in October and early November 1999 are analyzed to describe the Persian Gulf Water (PGW) core and the regional circulation in the Gulf of Oman. The warm and salty PGW core flows out of the Strait of Hormuz heading southeastward unto (25¿20'N, 57¿E), approximately. From there, it cascades down the continental slope, veers southwestward, and joins the Omani coast near (24¿50'N, 56¿50'E) to form a slope current. This PGW current has then thermohaline maxima on isopycnal σ0 = 26.5, near 220 m depth. Its thermohaline characteristics decrease along its progression to Ra's al Hadd (and then offshore into the Arabian Sea) but maintain a sharp contrast with surrounding waters. Outflow variability at the Strait of Hormuz can be related to downstream fluctuations of the thermohaline maxima in the PGW core at gulf scale and over a 2- to 3-week period. Moreover, several mechanisms (baroclinic instability, flow intermittency, cape effects) are examined to explain the widening of this PGW core upstream and downstream of Ra's al Hamra. In the eastern part of the Gulf of Oman, the regional circulation is a cyclonic gyre. The circulation in the western part of the Gulf is more complex, with the outflow of PGW and southeastward currents in the upper 250 m near the Omani coast, and a recirculation of upwelled waters near Ra's Jagin (on the Iranian coast). The large cyclonic gyre occupies at least the upper 300 m of the water column and undergoes little variation over a month. The PGW outflow in the northern Arabian Sea is southward and located 50--100 km from the coast. It borders a shallower northward current located offshore.