VESPA (Vehicular Event Sharing with a mobile P2P Architecture) is a system designed for vehicles to share information in inter-vehicle ad-hoc networks. The originality of VESPA is to support any type of event (e.g., available parking spaces, accidents, emergency braking, obstacles in the road, information relative to the coordination of vehicles in emergency situations, etc.) in the network. VESPA relies on the computation of an Encounter Probability (EP) to determine whether a vehicle is expected to meet an event or not. Then, according to that encounter probability, the system decides if the driver has to be warned. The Encounter Probability is also used in VESPA to perform an efficient dissemination of information between vehicles when they encounter each other.The use of the Encounter Probability allows to adapt the dissemination protocol to the type of information diffused in the network (vehicles behind, all the vehicles located inside a determined geographical area, etc.).