Resource contention on shared resources occurs when workload demands exceed the aggregate capacity of shared resources in the community. The token-exchange incentive scheme is traditionally employed to motivate organizations to contribute sufficiently to the community, as a means to minimize free riding. The same incentive scheme can concurrently be used to serve as a mechanism for performing admission control on jobs submitted by users. However, due to the likelihood of fluctuations in demand for computing resources, the initial assignment of tokens on the basis of each organization?s resource contribution, may have a significant impact on the performance trade-off between fairness and the system admission ratio. To address this problem, we extend the token-exchange scheme by designing trading policies that are responsive to the instantaneous degree of contention, so that, the trade-off between fairness and the admission ratio is less sensitive to the actual quantity of tokens assigned to each organization.