What is the value of DeltaG in a spontaneous reaction

Gibbs free energy of a reaction (Δ G) is the change in free energy of a system that undergoes the chemical reaction. It is the energy associated with the reaction, which is available to do some useful work. If ΔG0, then work has to be done on the system or external energy is required to make the reaction happen. ΔG=0 when the reaction is at equilibrium and there is no net change taking place in the system.

I believe that DeltaG is negative for a spontaneous reaction.