This guy is a pretty good, fairly level headed, source for commentary on the oil and gas industry:
It's interesting to see why the Strait of Hormuz is a problem. Basically he points of that there are chokepoints due to water depth and a couple of those choke points are in, or border right on the Iran side of the strait. His point is that it really is a problem if it is a prolonged attempt to make using the strait problematic. So that would mean more money spent to intervene to keep ships safe, plus increased insurance costs.
If it isn't too prolonged (months instead of a year or more) then things could settle back down fairly quickly. However if Iran goes ahead and tries to close it again, then in the short term there will probably be a spike in the price of oil and gas.