In the negotiation literature we find two relatively distinct types of negotiation. The two types are known as integrative negotiations and distributive negotiations. Integrative negotiations are those where all sides are looking for solutions that are "good" for everyone while distributive negotiations are those where each party tries to maximize his gain. In this paper we are interested in argumentation- based integrative negotiations. More precisely we present a study characterizing the outcomes of such negotiations. For this reason, we aggregate the argumentation systems that the agents use in order to negotiate. The aggregate argumentation system represents the negotiation theory of the agents as a group and corresponds to the "ideal" situation of having access to complete information or negotiating through a mediator. We show that the aggregation operator we use is very suitable for capturing the essence of integrative negotiation as the outcomes of the aggregate theory we obtain have many appealing properties (e.g. they are Pareto optimal solutions).