Bacău (bäkŭˈŏ) [key], city (1990 pop. 197,1921), E Romania, in Moldavia, on the Bistriţa River. The administrative and industrial center of an oil-producing region, Bacău has a papermill, textile factories, and industries that manufacture military planes. Although probably settled in the 5th cent., Bacău did not become important until oil was discovered there in the 20th cent. It has a regional museum and ruins of a 15th-century princely court.