The amount of oil that can be recovered during retorting varies with the oil shale and the technology used.[1] About one sixth of the oil shales in the Green River Formation have a relatively high yield of 25 to 100 US gallons (95 to 379 l; 21 to 83 imp gal) of shale oil per ton of oil shale; about one third yield from 10 to 25 US gallons (38 to 95 l; 8.3 to 20.8 imp gal) per ton. (Ten US gal/ton is approximately 3.4 tons of oil per 100 tons of shale.)