Coincidence processing in positron emission tomography (PET) is typically done during acquisition of the data. However, on the EXPLORER total-body PET scanner we plan, in addition, to store unpaired single events (i.e. singles) for post-acquisition coincidence processing. A software-based coincidence processor was developed for EXPLORER and its performance was assessed. Our results showed that the performance of the coincidence processor could be significantly impacted by the type of data storage (Peripheral Component Interconnect Express (PCIe)-attached solid state drive (SSD) versus RAID 6 hard disk drives (HDDs)) especially when multiple data files were processed in parallel. We showed that a 48-thread computer node with dual Intel Xeon E5-2650 v4 central processing units (CPUs) and a PCIe SSD was sufficient to process approximately 120 M singles s-1 at an incoming singles rate of approximately 150 Mcps. With two computer nodes, near real-time coincidence processing became possible at this incoming singles rate.