Ploiești (UK: ploy-ESH-tee, US: plaw-YESHT-ee, Romanian: [ploˈjeʃtʲ]), formerly spelled Ploești, is a city and county seat in Prahova County, Romania. Part of the historical region of Muntenia, it is located 56 km (35 mi) north of Bucharest.
The area of Ploiești is around 60 km2 (23 sq mi), and it borders the Blejoi commune in the north, Bărcănești and Brazi communes in the south, Târgșoru Vechi commune in the west, and Bucov and Berceni communes in the east. According to the 2011 Romanian census, there were 201,226 people living within the city limits, making it the ninth most populous in the country.
The city grew beginning with the 17th century on an estate bought by Michael the Brave from the local landlords, gradually taking the place of the nearby Wallachian fairs of Târgșor, Gherghița and Bucov. Its evolution was accelerated by heavy industrialisation, with the world's first systematic petroleum refinery being opened in 1856–1857.