The decision of accounting 174 billion barrels (28×10^9 m3) of the Alberta oil sands deposits as proven reserves was made by the Energy Resources Conservation Board (ERCB), now known as the Alberta Energy and Utilities Board (AEUB).[6] Although now widely accepted, this addition was controversial at the time because oil sands contain an extremely heavy form of crude oil known as bitumen which will not flow toward a well under reservoir conditions. Instead, it must be mined, heated, or diluted with solvents to allow it to be produced, and must be upgraded to lighter oil to be usable by refineries.[6] Historically known as bituminous sands or sometimes as "tar sands", the deposits were exposed as major rivers cut through the oil-bearing formations to reveal the bitumen in the river banks.