The objectives of this work are the development and design of controllers for a team of agents that accomplish consensus for agents' output in both leaderless (ILL) and modified leader-follower (MLF) architectures. Towards this end, a semi-decentralized optimal control strategy is designed based on minimization of individual cost functions over a finite horizon using local information. Interactions among agents due to information flows are represented through the control channels in characterization of the dynamical model of each agent. It is shown that minimization of the proposed cost functions results in a modified consensus algorithm for LL and MLF architectures. In the latter case, the desired output is assumed to be available for only the leader while the followers should follow the leader using information exchanges existing among themselves and the leader through a predefined topology. Furthermore, the performance of the cooperative team under a member's fault is formally analyzed and investigated. The robustness of the team to uncertainties and faults in the leader or followers and adaptability of the team members to these unanticipated situations are also shown rigorously. Finally, simulation results are presented to demonstrate the effectiveness of our proposed methodologies in achieving prespecified requirements. (C) 2008 Elsevier Ltd. All rights reserved.