TransAlta Corporation (formerly Calgary Power) is an electricity power generator and wholesale marketing company headquartered in Calgary, Alberta, Canada. It is a privately owned corporation and its shares are traded publicly. It operates over 70 power plants in Canada, the United States and Australia. TransAlta operates geothermal, wind, hydro, natural gas and coal power generation facilities. The company has been recognized for its leadership on sustainability by the Dow Jones Sustainability North America Index, the FTSE4Good Index and the Jantzi Social Index. TransAlta is Canada's largest investor-owned renewable energy provider. TransAlta, on several occasions, illegally manipulated the energy market to drive up power prices.