Plain water when boiled will never boil over the edge of the pot, because the bubbles will pop before they reach the surface. By adding olive oil to the boiling water, the surface tension is interrupted, thereby preventing the water from foaming up and boiling over the pot. By adding oil to the water, the oil helps form a top layer on the boiling water surface. This layer prevents the formation of foam, which otherwise would spill over the side of the pot.
Why does adding oils to cooking water keep it from boiling over?
