Out-of-order packet processing in a wireless communications system (WCS) is provided. A reordering queue is established for each data session to temporally hold an incoming data packet(s) until an out-of-order data packet(s) is received or discarded. A reordering timer is initiated to define a lifespan of the earliest detected missed data packet in the data session. If the earliest detected missed data packet is received before the reordering timer expires, the received data packet will be forwarded to a core network together with any subsequent in-order data packet(s) in the reordering queue. Otherwise, the missed data packet is discarded, the subsequent in-order data packet(s) in the reordering queue is forwarded to the core network, and the reordering timer may be redefined for a next missed data packet in the data session. Hence, it is possible to process out-of-order data packets for multiple data sessions with reduced processing complexity and latency.