The particle physics community is sharing its resources over a Grid network. Currently resources are used on availability. But there is no fair allocation considering the importance or the private value of a job. Researchers are using Grid resources regardless of whether others need them more urgently. Furthermore, they do not even provide their own resources as they do not have an incentive for sharing them. Researchers are demanding a Grid infrastructure where an incentive mechanism is implemented. This will support a fair allocation of resources. Incentives can be provided by using money. But one constraint is that no real money should be involved for billing the resources in the science community. In this paper, a mechanism called Token Exchange System (TES) is proposed. Considering the requirements from the particle physics community this mechanism combines the advantages of reputation and payment mechanism in one coherent system to realize a fair allocation. It enables to build up a Grid infrastructure with an incentive mechanism which is scalable, incentivecompatible and does not require a face-to-face agreement like the current system.