Barring the purchase of Iranian oil will decrease oil availability and thus increase oil prices. Instead, the West should impose a special tax on Iranian oil, say 5-10 dollars per barrel. The Iranians will be forced to discount their oil (absorb the tax) to make it sellable, so in effect the tax will be paid by Iranian treasury. Overall, the West will get extra income and Iran less. Iran will be forced to produce and sell even more oil. This will also lower world prices.
Report: Iran's Culture Ministry refuses to allow Barenboim to perform in Tehran (DPA)