The Athabasca tar sands with an oil content of 626 x 109 barrels are mined since 1967 in large scale operation. The opening up work in SYNCRUDE's Mildred Lake Pit started in 1974. The selected mining method and the unfavourable climatic conditions require a tailor-made design of the bucket wheel units for SYNCRUDE. The design features resulting from the mining method are described and compared with the one of bucket wheel excavators working in Lignite open pit mines. The dependency of design details from the climatic conditions is shown.