Despite Iran's threat to close the Strait of Hormuz, some global oil prices fell. It turns out Iran's influence on the international oil market may be weak, and its threats more an effort to head off international sanctions that will harm its own weakened petroleum economy. Shipping lanes are just one of many major strategic factors affecting the global oil market. Iran has, however, offered spurious ammunition to U.S. politicians crowing for US acts of war against it. Right now, the news media are taking Iran's threats more seriously than the oil market is.
"World oil prices sank in volatile year-end deals on Wednesday, as traders took profits and eyed the strong dollar, new concerns over the eurozone debt crisis and fresh equity falls on Wall Street.
New York's main contract, light sweet crude for February delivery, known as West Texas Intermediate (WTI), sank $1.98 to $99.36 a barrel.
Brent North Sea crude for February dived $2.16 to $107.11 in volatile late afternoon London trade, ahead of the New Year holiday break."
AFP had the story December 28, 2011. 
"US Warns Iran Over Threat To Block Oil Route" (BBC)
"U.S. Warns Iran Against Closing Hormuz Oil Route" (USA TODAY) 
"Iran Unlikely To Block Oil Shipments Through Strait of Hormuz, Analysts Say" (Washington Post) 
"Second Iranian Official Says Regime Could Close Gulf To Oil Traffic" (Los Angeles Times)
"Oil Above $107, U.S. Stocks and Iran in Focus" (Reuters)
"If Iran Moves, the USA Has No Plan for an Oil Interruption" (Huffington Post/Edwin Black)