Coatzacoalcos (kwätsäkwälˈkōs) [key], city (1990 pop. 198,817), Veracruz state, E central Mexico, at the mouth of the Coatzacoalcos River. It is a port on the Gulf of Campeche, as well as the northern terminus of rail traffic across the Isthmus of Tehuantepec. Highway communications are also good. The city is an important commercial center; oil, sulfur, and timber are exported.