In general, power plants operating below their maximum output can provide ramp-up capability, but in that case, they lose some revenues as they do not sell all the power they could produce on the energy market. Arbitrage links energy market prices with balancing and ancillary services prices and this creates opportunities to change the operations of generating units according to price incentives delivered on these different interrelated power markets. The market for reserves or balancing services may not have any locational dimension. Generation services are much more differentiated than the basic underlying commodity with which they are associated. The system operator may, for example, need generating capacity responding in 10 minutes at a particular node of the network (Joskow, 2007).