The interfacial tension represents a key quantitative parameter to control the compatibility of polymer blends processed by extrusion techniques and tune their final morphologies/properties. However, the evaluation of the interfacial tension between polymers in the melt state is still challenging with many experimental difficulties, especially for polyolefin-based blends. Here, two complementary techniques (i.e. rheological and optical methods) were selected to evaluate the interfacial tension between several polyolefins in the melt state. In particular, interfacial/surface tensions at 200°C between several types of polyethylene (PE)/isotactic polypropylene (iPP) (i.e. Ziegler Natta- and metallocene-catalyzed PE/iPP grades) are specifically addressed to detect slight variations in terms of melt compatibility and to highlight the role of metallocene polyolefins. Classical dynamic rheology experiments coupled to morphological analyses were first attempted and several trends are clearly observed in term of PE/iPP interfacial tensions. Metallocene PE/iPP associations display the lowest interfacial tension (0.8 – 1.1 mN/m) but actual values could not be unambiguously confirmed by optical methods using the polymer-in-polymer pendant drop method due a poor melt density difference. However, surface tensions in the melt state directly obtained by the pendant drop method provide a precise insight on polyolefin compatibility with an excellent sensitivity regarding the polyethylene catalysts used for synthesis. This work not only highlights the enhanced compatibility between metallocene polyolefins in the melt state but also demonstrate the efficiency of various tools for further predictions/optimization of the polymer/polymer interfaces without specific use of interfacial compatibilizers.