We discuss on purely analytical grounds the various mechanisms for electron acceleration, which can be relevant in the Petawatt laser pulse regime. This includes a modified version of the well-known wakefield acceleration (dominant for short pulses), stochastic acceleration due to counter-propagating laser pulses (which could be dominant for long pulses) and the relativistic photon mirror or the snow-plow effect (which could lead to enhanced single step acceleration). We discuss other stochastic processes related to the interaction between direct and wakefield acceleration. Approximate analytical criteria for stochastic and enhanced acceleration regimes are established. Our discussion also includes excitation of unstable betatron oscillations. The present analytical models could be relevant to the interpretation of both simulations and experiments.