The paper proposes decentralized deconfliction algorithms deployed on multiple autonomous aerial vehicles in freeflight operations. The paper provides two separate algorithms for collision avoidance - one based on the iterative peer-to-peer negotiation solving a singular collision and second based on multi-party negotiation about a cluster of collisions. The presented decentralized algorithms allow the vehicles operating in the same area to utilize the given airspace more efficiently. The algorithms have been developed and tested on a multi-agent prototype and the properties of both algorithms are discussed on a set of large scale experiments. Categories and Subject Descriptors I.2.11 [Computing Methodologies]: Artificial intelligence-Multi-agent systems; I.6 [Computing Methodologies]: Simulation and modeling General Terms Algorithms, Performance Keywords agent-based collision avoidance, autonomous aircrafts, distributed algorithm