Nanoparticles are promising materials to replace nocuous additive molecules currently used in engine oils. They present the advantage to easily enter the contact area and to be immediately active, even at ambient temperatures. A discussion covers the case of spherical nested carbon structures (carbon nano-onions CO). a new kind of nanoparticles with interesting tribological properties in both dry and lubricated wear; uniform dispersion of CO; reduction of both friction coefficient and wear under boundary lubrication; reduction of wear; presence of lubricious iron oxide materials in the wear particles; and the importance of rolling-to-sliding ratio in the lubrication process. This is an abstract of a paper presented at the 2009 World Tribology Congress (Kyoto, Japan 9/6-11/2009).