A. Haro, R. de la Llave How relevant are KAM tori in chains of coupled oscillators? (787K, Latex2.0 Revtex 3.1 with eps) ABSTRACT. We argue that to explain lack of equipartition of energy in chains of coupled oscillators, besides KAM tori, one should consider also secondary tori. Indeed, in certain regimes, we present a quantitative prediction of the relative abundance of these secondary tori which implies that secondary tori occupy much more measure than the KAM tori. This quantitative prediction is confirmed in numerical experiments.