Recent studies re-underline the role of localised inter-firm networks in innovation dynamics and economic performances of small firms. Farmer-owned co-operatives are supposed to benefit from local networking, but research has still to be done. In this paper we propose to combine economy and economic sociology to assess the structure and the role of specific informal inter-firm relations in a cluster of co-operatives : the advice networks between co-operative managers. Our study is based on the case of 31 co-operatives, constituting a wine cluster around Beziers (Languedoc, South of France). Using both sociometric and economic data, we find correlations between co-operatives relational and economic scores. The networks structure allows inter-firm co-operation on technical topics, but seems to limit exchanges in other strategic domains like marketing. Our results lead to action perspectives in co-operatives clusters and call for further collaboration between economy and sociology to analyse the relational and cognitive bases of co-operatives innovation dynamics and performances.