Solid and liquid lubrication play a key role in reducing energy consumption and wear behaviour of mechanical parts. Regarding the high importance of Diamond-Like-Carbon coatings, it is necessary to investigate their friction mechanism in lubricated conditions. In such contact, a complex "chemical reactor" is operating under severe dynamic conditions. The reason based on mainly the possibility of breaking of C-H and C-C bonds under the effect of shear, which leads to the emergence of C° free radicals or "dangling bonds" and a wide variety of tribochemical reactions follows. It was showed that rigid sp3-hybridized ta-C film lubricated in presence of ZDDP shows significant wear, associated with the absence of phosphate-type tribofilm. The wear is related to a preferential reactivity between the sulfur and the reactive carbon atoms from film surface. In contrast, hydrogenated DLC and a-C, show much lower wear and the formation of tribofilms with higher friction coefficient. Thus, the decomposition of ZDDP appears to be governed by contact pressure at asperity scale, but the surface and subsurface sulfur transport that leads to tribofilm formation or significant wear, depends on both stiffness and surface chemistry. Thus, the objectives of this study are to investigate the reactivity of four different DLC coatings representative of the variety of DLC found on the market and industrial applications such as a-C, a-C:H(20), a-C:H(40) and ta-C. Gas phase lubricated friction experiments are performed using a specific device, named Environmentally Controlled Analytical Tribology platform. They are carried out from Ultra High Vacuum to a few mbar by introducing gaseous sulphur-containing molecules to evaluate the reactivity of the different DLCs. In situ electronic spectroscopies are then performed on the tribofilms formed on the DLC surfaces, in addition to ex situ FIB/TEM/EELS analyses with particular attention on hybridisation state.