In 1999, the Texas Legislature passed a deregulation law that made it possible for consumers in most parts of Texas to choose their own electric company. Some areas, such as municipalities and cooperatives, were not required to deregulate, so customers in those areas may not have electric choice. TriCounty is an example of a cooperative where their members do not have a choice on their electric retail provider. Southlake residents in an Oncor service area have a separate electric retail provider such as TXU or Green Mountain Energy. You can also find more information here: https://www.currentutilities.com/how-it-works-texas-electricity/.