The aim of this work is to present a numerical measure of the importance of each player in a cooperative game when the cooperation possibilities are limited according to the links of an oriented network. The proposed concept of accessibility tries to conjugate the marginal contributions of each node as a game player with the cooperation geometry imposed by the digraph that models the network. We study general properties of this concept. KEYWORDS Game theory; Digraph; Accessibility; Cooperative game; Shapley value.