Dark energy and the generalized second law

We explore the thermodynamics of dark energy taking into account the existence of the observer's event horizon in accelerated universes. Except for the initial stage of Chaplygin gas dominated expansion, the generalized second law of gravitational thermodynamics is fulfilled and the temperature of the phantom fluid results positive. This substantially extends the work of Pollock and Singh [M.D. Pollock, T.P. Singh, Class. Quantum Grav. 6 (1989) 901] on the thermodynamics of super-inflationary expansion.