In the ongoing process to create a competitive electricity market, the prob
lem of Ancillary Services is assuming a fundamental role. Ancillary Service
s are those services performed by generators, transmission and control equi
pment, which are necessary to support basic services and to maintain reliab
le operations and system security. In this paper, we focus our attention on
one of these services, load following, and propose a competitive way to pr
ovide this service through bilateral contracts between supplier and custome
r. In general, we assume that there will be both a competitive market for t
he provision of load following and an authority responsible for the amount
of load following not met by bilateral contracts.