A mathematical model of a Once-Through Multi-Stage-Flash (OT-MSF) desalination system is developed. This study shows the impact of top brine temperature (TBT) of up to 160 degrees C on both the design and performance characteristics of MSF systems. Such a high TBT can be achieved by nanofiltration pretreatment to remove scale forming compounds. System performance is evaluated by the thermal performance ratio (PR) and the required specific area (sA). For a fixed brine reject temperature (T-end) and inter-stage temperature drop (Delta T), adding stages results in the TBT increasing by Delta T for each stage added and the PR increases monotonically with the TBT. On the other hand, the required sA decreases and then increases again beyond a certain TBT. The Sirte desalination plant in Libya is taken as a case study. It is found that by increasing the TBT to 161 degrees C from a typical value of 118 degrees C keeping T-end and Delta T fixed; the PR can be increased by 41.5%, reaching a value of 14.6 while the required sA increases by 0.9%. Although there is a penalty in terms of the increased number of stages required to achieve this arrangement, there is a clear advantage in terms of PR, with a relatively small compromise in sA. (C) 2017 Elsevier B.V. All rights reserved.