Today high volume of goods and services is being traded us-ing online auction systems. The growth in size and complexity of archi-tectures to support online auctions requires the use of distributed and cooperative software techniques. In this context, the agent software de-velopment paradigm seems appropriate both for their modelling, devel-opment and implementation. This paper proposes an agent-oriented pat-terns analysis of best practices for online auction. The patterns are in-tended to help both IT managers and software engineers during the re-quirement specification of an on-line auction system while integrating benefits of agent software engineering.