Norway has shown robust growth in economy since the start of the industrial era. Shipping has long been a support of Norway's export sector, but much of Norway's economic growth has been fueled by an abundance of natural resources, including petroleum exploration and production, hydroelectric power, and fisheries. The public sector is among the largest in the world as a percentage of the overall gross domestic product. Main exports of Norway are petroleum and petroleum products, machinery and equipment, metals, chemicals, ships and fish.