what is the difference between substrate level phosphorylation and oxidative phosphorylation?

Substrate-level phosphorylation occurs during Glycolysis and the Kreb's Cycle and involves the physical addition of a free phosphate to ADP to form ATP. Oxidative phosphorylation, on the other hand, takes place along the electron transport chain, where ATP is synthesized indirectly from the creation of a proton gradient and the movement of these protons back accross the membrane through the protein channel, ATP synthase. As the protons pass through, ATP is created.