Recently, ontologies have been developed in various business domains with the recent maturing of the Semantic Web technologies. However, ontology-related researches have largely focused on the facilitation of successful matchmaking but not much on traders’ requirement elicitation and potential negotiations in e-marketplaces. Because ontology provides the key knowledge about the inter-relationships among the issues and alternatives of the traders’ requirements, we show how to elicit trade requirements, alternatives, and tradeoff from an agreed ontology. This facilitates the whole business process of the e-marketplace, from matchmaking, recommendation, to negotiation. We further propose a novel methodology for the elicitation of dependencies among traders’ requirements for the formulation of an effective decision plan. As a result, traders can have a better cognition of their requirements and the overall operations of the e-marketplace can be streamlined.