The current air traffic management (ATM) system will soon reach its capacity limits, so new concepts for the future are being developed. Many proposed schemes include shifting the task of maintaining safe distances between aircraft to ground-based automation and assigning air traffic controllers a supervisory role. This research investigated air traffic controller performance using advanced ATM concepts for the task of conflict resolution. Performance using a medium fidelity air traffic control simulator was investigated across 2 proportions of free-flying traffic and 3 types of decision support. Conflict resolution performance was significantly degraded when free-flying aircraft failed to negotiate a conflict and controllers had to intervene. Conflict resolution performance varied across the aiding condition and was superior when negotiation information was provided. However we did not find any differences in performance across proportions of free-flying traffic. Implications of this research are in further exploration of ATM concepts, design of decision aids, and training needs assessment.