The approach that's being used—it's been tested in Quebec and also in New Brunswick—tends to be liquefied petroleum gas, basically a propane frac. That method offers a number of advantages in terms of management of the flow-back of the fluid, the fluid in this case being propane. It can either be recovered or, depending on the quantity that's coming back, left in the gas stream for recovery at gas plants.
Safety is probably one of the key issues around using propane, although it's being used in many places. It has been used in Alberta for a number of years, and the procedures are well understood. But unlike water, propane has some additional risks.