Grids aim at exploiting synergies that result from cooperation of autonomous distributed entities. For this cooperation to be sustainable, participants need to have economic incentive. Within service-oriented Grids, resources may be advertised and traded as services, and QoS requirement is the most important attribute. In this paper, we build on two intellectual threads: market-based approaches and the economic theory of utility to resource allocation. We consider the problem of task scheduling subject to time and budget constrains as QoS-aware joint utility function, and scheduling object is to maximize total attained utility. This scheduling problem can be shown to be NP-hard, thus we present a utility-driven heuristic scheduling algorithm (UDS) for this problem. We study the performance of UDS algorithm through a Stochastic Petri Net (SPN) model. In the end, the performance of model is analyzed by SPNP software package. The numerical results show that UDS can guarantee QoS for users.