What do US sanctions on Iran mean for OPEC?

Even though we doubt that the US sanctions will cause a large fall in Iran’s oil output, the rest of OPEC and Russia have enough spare capacity to prevent a shortage if US sanctions turn out to be more restrictive than we think. However, a sharp drop in Iranian output could prevent total OPEC output from rising next year, even if the group abandoned its quotas, and would require us to raise our price forecast.