Gebze (Turkish pronunciation: [ˈɟebze]), formerly known as Libyssa, is a working-class district and one of the municipalities in Kocaeli Province. Its area is 418 km, and its population is 407,019 (2022). It is situated 65 km (30 mi) southeast of Istanbul, on the Gulf of Izmit, the eastern arm of the Sea of Marmara. Gebze is the largest district by population size in the province as of 2022, exceeding İzmit, the provincial capital. Its population consists of a colossal working class, one of the largest in Turkey, as it hosts 10 industrial parks, in which hosts 1,384 companies and over 130,000 people are employed.