Throughout the twentieth century, manufactured coal gas was gradually replaced by natural gas. In many cases there was a transition period where distributors sold mixtures of synthetic and natural gas, and only later switched to pure natural gas. Although manufactured gasworks in Singapore and Hong Kong still use the combined gas – they have not yet converted to pure natural gas. In addition, during these transition stages, some of the coal gasworks were retained for extended periods to help with peak loads, but were gradually replaced with LNG storages. In the process of converting original manufactured gas, distribution networks were also often converted to transport natural gas to end-users. Appliances and machinery that used manufactured gas were also converted, with fi nal sellers of natural gas often assisting in the conversion of gas appliances.