Thirty-six (36) separate and distinct public universities exist in Texas, of which 32 belong to one of the six state university systems. Discovery of minerals on Permanent University Fund land, particularly oil, has helped fund the rapid growth of the state's two largest university systems: the University of Texas System and the Texas A&M System. The four other university systems: the University of Houston System, the University of North Texas System, the Texas State System, and the Texas Tech System are not funded by the Permanent University Fund.