The Generalized Second Price (GSP) auction is the primary auction used for
monetizing the use of the Internet. It is well-known that truthtelling is not a
dominant strategy in this auction and that inefficient equilibria can arise. In
this paper we study the space of equilibria in GSP, and quantify the efficiency
loss that can arise in equilibria under a wide range of sources of uncertainty,
as well as in the full information setting. The traditional Bayesian game
models uncertainty in the valuations (types) of the participants.