In this paper we discuss the possibility of applying the various game-theoretic mechanisms to support the postnegotiation analysis of the multi-issue two-party negotiation. We analyze the negotiation problem stucturized and evaluated by parties by means of the simple additive weighting model, which is typical approach implemented in very many negotiation support systems. In particular, we focus on such negotiation processed that result in an inefficient negotiation outcome. We show how to identify the set of efficient solutions for each negotiation problem and then, how to find the efficient improvements of the agreement that the parties have agreed on. We propose a novel mechanism of finding such improvements, that stems from Nash bargaining solution and some previous concepts of Raiffa's potentials of the negotiators. We show an example of how this mechanism works when applied to find an improvement in bilateral negotiation supported by Inspire negotiation support system.