  We describe an efficient incentive mechanism for P2P systems that generates a
wide diversity of content offerings while responding adaptively to customer
demand. Files are served and paid for through a parimutuel market similar to
that commonly used for betting in horse races. An analysis of the performance
of such a system shows that there exists an equilibrium with a long tail in the
distribution of content offerings, which guarantees the real time provision of
any content regardless of its popularity.
