The profitability of generating units that are likely to operate only for a relatively small number of hours in each year (peaking capacity) is especially sensitive to the level of prices that are realized during the small number of high demand hours in which they provide energy or operating reserves. Figure 21 shows the notional revenues calculated for a peak power plant in Australia. A gas fired power plant running only when prices are above 1000 AUS$/MWh would have earned revenues above annual costs only two years in the period 2006-2011, corresponding to two dry years.