Quote from achilles28:
I think part of this is an extension of the Arab Spring. Two birds with one stone. Pressure from above, pressure from below. The pressure from above is US military. Pressure from below, are domestic riots/civil insurrection spurred by (even) higher crude costs, against middle eastern Governments the US wants deposed.
Also, if OM77 is right about Iranian oil production accounting for 20% of global output, how can the Saudis and Libya make up that shortfall. That's a tonne.
Ex a blockade the oil would continue to flow, just to Asia. So Libya/SA would only have to make up for whatever shortfall there is in Iran's sales that would impact global prices.
The idea is to shrink the market for Iran's crude, not make them stop pumping. Only Iran gets hurt that way.