Monitoring of active goaf seals at Mandalong Mine shows anomalous levels of ethane concentrations. Currently ethane concentrations exceeding 250 ppm have been experienced from 30 to 32 C/T seals of MG8 with the remainder of the panel averaging 50 - 100 ppm. Active goaf seals for MG7 and MG9 average 50 - 100 ppm and 80 - 100 ppm, respectively. For most mines these concentrations of ethane would be assumed to indicate a spontaneous combustion event; however no carbon monoxide is being recorded and a sympathetic relationship with methane indicates that the measured ethane is due to gas desorption. This paper presents the results from the mine showing trends in ethane emissions from the active goaf seals to date, and shows how this historical data can be used to predict expected ethane concentrations in the active goaf of MG10.