  We consider spherically symmetric Einstein-massless-scalar field equations
with negative cosmological constant in five dimensions and analyze evolution of
small perturbations of anti-de Sitter spacetime using the recently proposed
resonant approximation. We show that for typical initial data the solution of
the resonant system develops an oscillatory singularity in finite time. This
result hints at a possible route to establishing instability of AdS under
arbitrarily small perturbations.
