DFW started with 17L on the east side and 17R on the west side. When the first set of parallels was built the east side runways became 17 left and right and the west side runways became 18s. There are plans for a short (by DFW standards) far west runway which would be 18R-36L and the current 18R-36L would be renamed 18C-36C. But there are noise concerns as flights for that runway would go over the center of the town of Grapevine to the north of the airport. And the demand for 6 parallel runways isn't there yet.