It was unexpectedly discovered that coal from the Morwell open cut mine, with its high alkali and sulphur content, was not suitable for briquetting. The briquettes deteriorated quickly and fouled the boilers. In order to produce usable briquettes, Yallourn coal had to be transported to supply the Morwell briquette factories on the interconnecting railway, which was an additional cost. At this time, a decline in demand for briquettes was becoming evident, due to competition from oil, electricity for domestic heating, and several years later, the discovery of natural gas in Bass Strait.