Ploieşti (ployĕsht´), city (1990 pop. 259,014), S central Romania, in Walachia. It is the chief center of the Romanian petroleum industry and of the Ploieşti oil region. The city is a railroad hub and is linked by oil pipelines with Bucharest and the ports of Giurgiu on the Danube River and Constanţa on the Black Sea. It has large refineries and oil storage installations and is an industrial center with varied manufactures. Founded in 1596 by Prince Michael the Brave of Walachia, Ploieşti grew in the 19th cent. into the largest oil-producing center of SE Europe. After Romania signed (1940) a mutual cooperation pact with the Axis powers that provided substantial Romanian oil to Germany, the Allies heavily bombed the city. An earthquake in 1940 also inflicted severe damage. After World War II, Romania nationalized the Ploieşti oil industry, which until then had been owned largely by foreign interests. Under Communist rule, massive investments in the petroleum and petrochemical industries were made in the drive to modernize.