of gas dropped to 11 cents per gigajoule, because of maintenance issues with the pipeline giant TC Energy Corp. In 2003 Alberta produced of marketable natural gas. That year, 62% of Alberta's natural gas was shipped to the United States, 24% was used within Alberta, and 14% was used in the rest of Canada. In 2006, Alberta consumed of natural gas. The rest was exported across Canada and to the United States. Royalties to Alberta from natural gas and its byproducts are larger than royalties from crude oil and bitumen. In 2006, there were 13,473 successful natural gas wells drilled in Alberta: 12,029 conventional gas wells and 1,444 coalbed methane wells. There may be up to of coalbed methane in Alberta, although it is unknown how much of this gas might be recoverable. Alberta has one of the most extensive natural gas systems in the world as part of its energy infrastructure, with of energy related pipelines. Coal Coal has been mined in Alberta since the late 19th century. Over 1800 mines have operated in Alberta since then. The coal industry was vital to the early development of several communities, especially those in the foothills and along deep river valleys where coal was close to the surface. Alberta is still a major coal producer, every two weeks Alberta produces enough coal to fill the Sky Dome in Toronto. Much of that coal is burned in Alberta for electricity generation. By 2008, Alberta used over 25 million tonnes of coal annually to generate electricity. However, Alberta is set to retire coal power by 2023, ahead of 2030 provincial deadline. Alberta has vast coal resources and 70 per cent of Canada's coal reserves are located in Alberta. This amounts to 33.6 Gigatonnes. Vast beds of coal are found extending for hundreds of miles, a short distance below the surface of the plains. The coal belongs to the Cretaceous beds, and while not so heavy as that of the Coal Measures in England is of excellent quality. In the valley of the Bow River, alongside the Canadian Pacific Railway, valuable beds of anthracite coal are still worked. The usual coal deposits of the area of bituminous or semi-bituminous coal. These are largely worked at Lethbridge in southern Alberta and Edmonton in the centre of the province. Many other parts of the province have pits for private use. Electricity , Alberta's generating capacity was