There has been a lot of talk lately about the potential for the Iranians to close the Strait of Hormuz in the event of conflict following an Israeli or US attack on Iranian nuclear facilities. The danger is definitely very real as the shipping lane is only 6 miles wide, so even a second rate military power could create quite a bit of havoc if it wanted to. However, any temporary closing of the Strait, and it would be temporary, probably won't have that much of an impact on our oil supplies in the medium to long term. Tankers that are bottled up in the Persian Gulf can be unbottled again once the US devotes enough sea and air power to destroy any threats.
However, what people don't seem to be talking about much is the threat to the Saudi oil fields themselves. Saudi Arabia accounts for about a quarter of the world's proven reserves and produces 11 million barrels per day of oil. As you can see in the map below, the oil producing fields, including the immense Ghawar (it can produce 5 million barrels per day by itself), are concentrated in the eastern section of the country, the section closest to the Persian Gulf:
Unfortunately, the Saudi oil fields are relatively close to Iran, which is just across the Gulf. But more importantly, take a look at this map of the Shia sections of Saudi Arabia:
As you can see, the Shia population of Saudi Arabia seem to be living right on top of the bulk of the oil resources of the country (conversely it seems that the Jews wandered 40 years in the desert and found the one place in the middle east without any oil). Importantly, the Shia in Saudi Arabia have been oppressed by the Wahhabi Saudis for decades so what do you think might happen if Shia dominated Iran comes asking for their help? My guess is a large minority will be happy to stir up trouble by attacking the Saudi oil fields. If the Iranians were smart they would have been smuggling weapons to sleeper cells there for years waiting for their moment. Once the fighting starts, I also wouldn't be surprised if some Iranian Revolutionary Guards come across the gulf or smuggle themselves in through Iraq (which has a Shia dominated government & military).
So while our forces are focusing on keeping the flow of oil going through the Strait of Hormuz, the actual source of the oil itself could be in some very real danger. Let's hope we have some contingency plan for this, hopefully one that doesn't date back to Operation Desert Shield.