In this paper, we present the overall design for an auctioning based resource trading/acquiring system that can be deployed in wide-area computing systems such as Grid systems. Selecting the winning bids is one of the core issues in any system that utilizes the auctioning paradigm. We identify the unique aspects of our system that impact the winner selection process. More specifically, the necessity to acquire or trade resources as a bundle (i.e., perform co-allocation) presents a challenge to traditional bidding mechanisms. We present a new bidding mechanism called “co-bids” to address this problem. Two heuristics for winner selection with co-bids are proposed. The performance of the heuristics are examined via simulations.