In this article, we consider the synchronization problem in a network of nonlinear multiagent systems having the same relative degree r. The agents do not have access to their state or output and only have relative output information from their neighbors. The controller structure is decentralized in nature and, therefore, depends only on the relative information available to it. The agent dynamics are transformed into relative dynamics by a change of coordinates where the agent dynamics are coupled. Extended high-gain observers are used to estimate the nonlinear coupling at each agent and then cancel them using feedback control. Therefore, the problem changes to a stabilization problem ofN nonlinear systems in the relative coordinates. It is shown that the agents achieve practical synchronization and the synchronization error can be made arbitrarily small by tuning the high-gain observer parameter. Finally, simulations are done with a network of power systems to show the efficacy of the proposed controller.