served as Sasol's first offices and is still in existence today. Coal mining To support the required economies of scale for coal-to-liquids (CTL) process to be economical and competitive with crude oil, all stages of the operations, from coal mining to the Fischer–Tropsch process and product work up must be run with great efficiency. Due to the complexity of the Lurgi gasifers used, the quality of the coal was paramount. The initial annual output from the Sigma underground mine in Sasolburg was 2 million tons. Annual coal production from this mine peaked in 1991 at 7.4 million tons. Today, most of the gasifiers in Sasolburg have been replaced with autothermal reformers that feed natural gas piped from Mozambique. Natural gas generates about 40–60% less carbon dioxide for the same energy produced as coal, thus is significantly more environmentally friendly. Gas-to-liquids technology converts natural gas, predominantly methane to liquid fuels. Today, Sasol mines more than 40 million tons (Mt) of saleable coal a year, mostly gasification feedstock for Sasol Synfuels in Secunda. Sasol Mining also exports some 2.8 Mt of coal a year. This amounts to roughly 22% of all the coal mined in South Africa. Underground mining operations continue in the Secunda area (Bosjesspruit, Brandspruit, Middelbult, Syferfontein, and Twistdraai collieries) and Sigma: Mooikraal colliery near Sasolburg. As some of these mines are nearing the end of their useful lives, a R14bn mine replacement program has been undertaken. The first of the new mines is the R3.4bn Thubelisha shaft, which will eventually be an operation delivering more than 8M tons/annum (mtpa) of coal over 25 years. The Impumelelo mine, which will replace the Brandspruit operation, is set for first production in 2015. It will be ramped up to produce 8.5 mtpa, and can later be upgraded to supplying some 10.5 mtpa. This coal will be used exclusively by the Sasol Synfuels plant. An underground extension of the Middelbult mine is also on the cards, with the main shaft and incline shaft being replaced by the Shondoni shaft. The first coal from the new complex was expected to be delivered in 2015. The Secunda collieries form the world's largest underground coal operations. In conjunction with the continuous improvement in the Fischer–Tropsch process and catalyst, significant developments were also made in mining technology. Coal mining at Sasol from the early days has been characterised by innovation. Sasol Mining mainly uses the room and