In the last few years, an overwhelming amount of agent-based systems for supporting business-to-customer (B2C) e-commerce activities have been proposed. In this context, the use of agent ontologies for modelling the realities of both customers and sellers may play an important role. This paper deals with a formal model of agent ontologies, capable of describing the entities involved in the above realities (products, product features, product categories) as well as the behaviour of customers and sellers in performing their activities. Furthermore, we present some techniques that exploit the proposed ontology model for supporting the various B2C e-commerce stages represented in the Consumer Buying Behaviour (CBB) model. Finally, we briefly describe the OBA_B2C multi-agent architecture that implements in a JADE-based environment all the proposed techniques.