The large-scale dynamic behavior of Mercury's highly compressed magnetosphere is predominantly powered by magnetic reconnection. Energy and momentum are transferred from the solar wind to the magnetosphere, driving the large-scale circulation of magnetic flux through the system predominantly via the substorm, or loading-unloading cycle. We will present a statistical analysis of the average amplitude, duration and frequency of these loading-unloading events using magnetic field data acquired in orbit about Mercury by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The largest amplitude loading-unloading events cycle through ~50% of Mercury’s open flux content. We will analyse the combination of magnetotail and solar wind parameters leading to these extreme events.