Since computationally intensive applications may often require more resources than a single computing machine can provide in one administrative domain, bolstering resource co-allocation is essential for realizing the Grid vision. Given that resource providers and consumers may have different requirements and performance goals, successfully obtaining commitments through concurrent negotiations with multiple resource providers to simultaneously access several resources is a very challenging task for consumers. The contribution of this work is devising a concurrent negotiation mechanism that (i) coordinates multiple one-to-many concurrent negotiations between a consumer and multiple resource providers, and (ii) manages (de-)commitments (intermediate) contracts between consumers and providers. Even though the mechanism in this work allows agents to decommit intermediate contracts by paying a penalty, it is shown that the decommitment mechanism is non-manipulable. In this paper, (i) three classes of commitment strategies for concurrent negotiation and (ii) a fuzzy decision making approach for deriving adaptive commitment management strategy profiles of a consumer are presented. Two series of experiments were carried out in a variety of settings. The first set of empirical results provide guidelines for adopting the appropriate class of commitment strategies for a given resource market. In the second set of experiments, consumer agents negotiated in n markets to acquire n resources where the market type for each resource is unknown to consumers (market types are defined by different supply and demand patterns of resources). Favorable results in the second set of experiments show that commitment management strategy profiles for a consumer derived using the fuzzy decision making approach achieved the highest expected utilities among all classes of commitment management strategy profiles.