The benefits of horizontal collaboration depend heavily on the flexibility that each partner allows in his delivery conditions through the creation of better and more efficient distribution plans. On the other hand, the sharing of savings is one of the main factors that can block the success of collaboration and produce, consequently, conflicts between partners. This paper argues that to achieve equitability, the sharing of collaborative savings must take into consideration the partners’ participation in sustainability and flexibility. Involving each partner's sustainability and flexibility when sharing the gains from horizontal collaboration is an effective way to persuade companies to relax their plans. First, the importance of including these two factors on the performance of horizontal collaboration is highlighted. The introduced approach consists in using the decomposition method to determine a sustainability and flexibility rate for each partner. Then, an allocation approach based on cooperative game theory (namely τ-value), is developed. It combines each partner's impact on sustainability and his level of flexibility in terms of delivery time. The obtained results show that the suggested approach can adjust the results of the traditional approach by preventing the partners from benefiting from each other.