This paper studies the contractual form in horizontal cooperative agreements -those in which all partners perforrn the activities of the agreement, sharing part of their assets- within a transaction cost framework. It is argued that joint ventures are preferred to contractual arrangements as the complexity of the cooperation increases. This is the case in the following situations: agreements with a high number of partners, with an uncertain duration, comprising several functional areas, and where, at least, one of the partners is seeking to learn from the rest. Those hypotheses have been confirmed through an analysis of 438 cooperative agreements.

Keywords: horizontal cooperative agreements, strategic alliances, joint ventures, contractual agreements, transaction costs.