We consider the final stage of double ionization Of 02 molecules by short linearly polarized laser pulses. The saddles of the effective adiabatic potential energy close to which simultaneous escape of electrons from a molecule takes place are identified. The analysis of the saddles and numerical simulations of the ionization indicate that, to observe clear signatures of simultaneous electron escape in double ionization of O-2 molecules, stronger and much shorter laser pulses than those used in the recent experiment.