  The $\pi$, $\eta$ and $\rho$ exchange contributions to the cross-section for
the reaction $pp\to pp\eta$ near threshold are calculated with a
phenomenological description of the intermediate S11 (N(1535)) resonance for
all exchange mechanisms. The final state interaction in the $pp$ system is
described by realistic nucleon-nucleon interaction models. The sensitivity of
the results to the phenomenological models for the $\eta$-nucleon transition
amplitude and the nucleon-nucleon interaction is explored. The $\eta$ exchange
mechanism is found to play a dominant role. The off-shell behavior of the $\eta
N \to \eta N$ amplitude within the $\eta-$exchange amplitude leads to a result
significantly different from that obtained with the constant scattering length
approximation. The two-nucleon amplitudes that are associated with the short
range components of the nucleon-nucleon interaction contribute significantly to
the cross section.

Nuclear Theory