The retail electricity market in Texas is undergoing consolidation as the biggest players gobble up smaller rivals. The pecking order hasn't changed in the shuffle - Houston and New Jersey-based NRG Energy is still the biggest, selling under brand names like Reliant Energy and Green Mountain Energy, while Irving-based Vistra Energy remains No. 2 with its TXU Energy brand. British-owned Centrica, owner of Direct Energy, comes in third.