The U.S. Antarctic Program uses tractors to transport fuel and some cargo between McMurdo and South Pole stations. The resupply mission is called the South Pole Traverse, and it follows a 1,000-mile-long compacted snow route that begins at sea level at McMurdo Station and climbs to 9,300 feet to Amundsen-Scott South Pole Station. The fuel is transported in soft-sided bladders that ride in special sleds that reduce friction as they are dragged across the snow surface. A round-trip between the two stations averages 50 days.