We assess limits on the maximum energy of protons accelerated within superbubbles, considering a number of detailed scenarios. In particular, we derive under which circumstances PeV protons
are to be expected. Large-scale turbulent outflows spread in the cavity are not found to accelerate particles beyond a few hundreds of TeV. We also show that primary shocks such as supernova remnants expanding in the low density medium or the collective wind termination shock which forms around a compact stellar cluster could barely accelerate PeV protons. A more promising scenario is the case of a supernova remnant shock expanding within the collective wind of a compact stellar cluster. We show that protons of several PeV could be produced. This provides a natural explanation for the galactic cosmic rays in the very-high energy range. On the other hand, the scarcity of these events make it unlikely to detect associated ultra-high energy gamma-ray sources.