In the past the process for sealing longwall goafs at Mandalong has been to simply seal access points to the goaf and monitor the goaf as it self inertised. Due to changes in legislative requirements an improved method was required. A number of different methods utilising N2 or CO2 have been utilised at other mine sites. However, at Mandalong it was decided to use methane from the in-seam gas drainage system to purge and inertise the goaf. According to our knowledge this is the first time this method of utilising methane for goaf inertisation and sealing has been implemented. The aim of the sealing process is to seal the goaf in a safe manner without disruption to other parts of the mine. This is achieved by controlling the inertisation process through the introduction of methane from the gas drainage system with the intent of purging the critical zone of the unsealed goaf of any oxygen. Methane from the mine’s gas drainage system and existing pipe arrangement is re-directed to the seals behind the longwall take-off face and injected into the goaf fringe under seam pressure. The goaf atmosphere is monitored via a tube bundle system and is allowed to enter and exit the explosive range under controlled conditions. When the tube bundle monitoring shows the goaf atmosphere is inert, final sealing of the goaf is carried out. The principal hazard associated with the sealing of a goaf area in a gassy mine is the ignition of an explosive atmosphere resulting in an explosion. To reduce this risk to as low as reasonably possible (ACARP) numerous controls are implemented. Mandalong has successfully utilised this method four times since February 2008. Longwall 5 (LW5), Longwall 6 (LW6), Longwall 7 (LW7), Longwall 8 (LW8) and Longwall 9 (LW9) were sealed in this manner, and it is intended future longwall goafs be sealed utilising the same methodology. The results of these will be presented and discussed.