The Western Intermediate Water (WIW) is one of the most important water masses in the Western Mediterranean Sea (WMED), as it significantly impacts the general circulation and water mass exchange and contributes to the ventilation of WMED. It is formed in the Gulf of Lion and the Balearic shelf during the winter-to-spring transition period. Prior studies characterized the thermohaline characteristics of the WIW either using fixed limits (salinity < 38.3 and temperature < 13°C) or alternative detection approaches based on the geometrical analysis of temperature-salinity diagrams. In this study, we aim to better understand the formation, properties, and 3-dimensional pathways of the WIW in the western Mediterranean. We combined more than 20,000 in situ profiles (gliders, floats, UCTD) from the CALYPSO 2022 experiment with numerical simulations from the regional models. Our results show that the WIW mostly spreads between the isopycnals 28.8 and 29.0 kg m^-3 and is (now) warmer and saltier than previously reported. We found that WIW is formed at various sites in addition to the northern WMED; its formation is not limited to the winter season, and it can be detected at depths of up to 500 m in the Balearic Sea and other areas of WMED. Also, we used oxygen as a semi-conservative tracer to identify the WIW signal in the Balearic region. We showed that dissolved oxygen (DO > 210 μmol kg^-1) can be used as a tracer of WIW during its lateral advection by the northern current or mesoscale processes into the Balearic Sea. To understand better the mechanisms involved in the WIW formation, we developed a 1-D buoyancy loss model to simulate WIW formation at different sites. The model can simulate the deepest mixing using existing CTD profiles and atmospheric fluxes. We conclude by showing that this model could have an important role in understanding the 3-dimensional pathways of the WIW as well as in simulating and predicting the oxygen content of the WIW after leaving the surface.