Sisak is a city in central Croatia, spanning the confluence of the Kupa, Sava and Odra rivers, 57 km southeast of the Croatian capital Zagreb, and is usually considered to be where the Posavina begins, with an elevation of 99 m. The city's total population in 2011 was 47,768 of which 33,322 live in the urban settlement.
Sisak is the administrative centre of the Sisak-Moslavina County, Croatia's biggest river port and a centre of river shipping industry. It lies on the D36 state road and the Zagreb-Sisak-Novska railway. Sisak is a regional economic, cultural and historical center. The largest oil refinery in Croatia is here.