This paper addresses the formal specification and verification of situated Multi-Agent Systems (MAS) that can be formulated within the Influence/Reaction model as proposed in 1996 by Ferber \& Muller. In this model, our objective is to prove the correctness of reactive MAS with respect to a certain formal specification or property, using formal methods. This is an important step to bring MAS to high quality standards as required for critical applications encountered in domains such as transport systems. A generic B representation of systems instantiating the Influence/Reaction model is proposed, using patterns of specification. We illustrate our approach with a MAS to control unmanned land vehicles to form a platoon. The papers ends with considerations about further improvements of the framework, involving simulation and study of the properties of the system.