Some procurement negotiations are difficult to conclude smoothly using existing information processing systems because they need to first develop fuller buying/supplying specifications through bilateral negotiations between the buyer and supplier. In this paper, we propose an e-procurement model that provides a specification improvement mechanism, whereby a buyer can improve his/her procurement specifications using the supplier's knowledge. We conducted a simulation based on a real procurement case study to establish the effectiveness of our e-procurement model. Simultaneous procurements using multi-agent based technology can help buyers improve their own specifications. In addition, the e-procurement model helps suppliers to enhance the order-acceptance potential.