If you're reading this, you've spent a meaningful portion of your life in a climate of tension between the U.S. and Iran. Along with the United States, a host of other nations, including Great Britain and Israel, have jousted at least verbally with the regime that assumed power in 1979 in the former seat of the Persian Empire.

Now, however, the fat is again in the fire between that nation and much of the rest of the world on a couple of fronts. It seems that Fools would be well advised to assess what effect emerging new stresses could have on their investments (energy and otherwise) -- not to mention their lifestyles. Last week, 15 British Royal Navy crew members were seized in waters that British and U.S. authorities maintain were 1.7 nautical miles inside Iraqi territory, but which Iranian authorities claim were within their own territorial limits.

The captured Brits have yet to be released, although there has been some speculation that their one female member could be freed in the near term. In the meantime, they have been paraded on Iranian TV, and it is anyone's guess how long the British will allow their military personnel to be held before invoking countervailing force against Iran.

And with international nerves obviously raw, crude oil prices shot up temporarily on Tuesday when it was reported briefly that U.S. and Iranian naval forces had become involved in a skirmish of their own. When the report was proven false, prices returned to their prior level -- just below $65 per barrel.

Ignoring the world
At the same time, Iran, under President Mahmoud Ahmadinejad, continues to thumb its nose at the rest of the world regarding the ordered cessation of is disputed nuclear program. Last weekend, Vladimir Putin and Hu Jintao, the presidents of Russia and China, respectively, somewhat surprisingly urged Iran to adhere to U.N. Security Council resolutions and International Atomic Energy Agency (IAEA) decisions demanding such a cessation. Also during the weekend, the Security Council voted to impose new sanctions on the rogue nation. Iran in turn rejected the sanctions and subsequently announced that it would partially suspend cooperation with the IAEA, the U.N.'s atomic watchdog.

As most Fools know, Iran sits in the midst of the Middle East's oil producing area, between Iraq and Afghanistan, across the Persian Gulf from Saudi Arabia, and south of Turkmenistan and the Caspian Sea. Its vast proved oil reserves, which, while far less than the Saudis', nevertheless position it among the world's top five in a statistic that admittedly tends to wax and wane depending upon who's doing the calculating and the specific timeframe upon which they're focusing.

Known as Persia until 1935, Iran became an Islamic republic more than a quarter-century ago, when its ruling monarchy was overthrown and Mohammad Reza Shah Pahlavi was forced into exile. Conservative clerical forces then established a theocratic system of government under Ayatollah Khomeini. In November 1979, in perhaps Iran's most noteworthy confrontation with the U.S., militant students seized the U.S. embassy in Tehran and held 52 embassy employees hostage for 444 days.

In the face of Iran's latest round of obstreperousness, there is increasing concern in the West about the possibility of Iranian-induced shenanigans in the Strait of Hormuz, the narrow inlet between the Persian Gulf and the Gulf of Oman that is under Iran's control. With nearly half the world's traded oil being hauled through the strait -- and with Iran having vowed to respond in "many ways" to any sort of Security Council pressure related to its nuclear program -- any sort of lingering blockage of the strait through the laying of mines or other means clearly would be catastrophic for the industrialized world.

Still in second place
Iran has long been a key member of OPEC, with daily production that, according to BP (NYSE:BP) statistics, has ranged from 3.4 million barrels a day in 2002 to nearly 4 million daily barrels in 2005. That's well less than half the crude being pumped by Saudi Arabia, the cartel's big enchilada. 

But despite Iran's ample energy supplies, its obstinacy may be fueled by difficulties that are more severe than we in the West realize. While its daily crude output appears to have fallen into the 3.7 million-3.8 million barrels range -- it also has ample deposits of natural gas -- its export levels have declined steadily to a current level of about 2.2 million barrels a day, since its domestic energy use has been climbing. The effects on its coffers have been so severe that Russian technicians recently stopped work on its Bushehr nuclear reactor project, reportedly because Iran had fallen behind on its payments. While those payments may have been resumed, the scenario has intensified the world's attention to this oil-rich, but possibly cash-poor, nation. 

This, of course, raises another vital subject in the Iranian conundrum: its changing relationship with Russia. The Wall Street Journal grappled with this issue earlier in the week, after the Russians surprisingly departed from their usual protectionist approach vis-a-vis Iran in the Security Council. This time, Russia sided with the U.S. and others determined to invoke punitive measures in response to Iran's nuclear policy.

The Journal's take was essentially that some elements in Russia are concluding that the nation would be well served by an increase in its cooperation with the major industrial states, especially the United States. A second rationale is that Russia is offering an unspoken and undesignated quid pro quo for earlier U.S. support of its entry into the World Trade Organization, "apparently for nothing."

I personally lean to the first explanation, but with a modifier: Russia's crude production increased dramatically over the past decade, before its giant Sakhalin-1 project had really lifted off. That makes the Russians easily the world's second-largest oil producer (behind only the Saudis), and substantially ahead of our own slowly dwindling levels. I'll bet Russia realizes that its world is progressively more defined by its expanding oil production and its partnerships with such western companies as ExxonMobil (NYSE:XOM), Royal Dutch Shell (NYSE:RDS-B) and BP.

All this may be pushing Iran to prove to the world -- including its now-uncertain Russian ally -- that it can puff out its chest and go it alone internationally. The danger, of course, is that it will take on the British or U.S. militarily, resort to mischief in the Strait of Hormuz, or induce Venezuela's Hugo Chavez to add critical mass to its threats.

And so the obvious question on the minds of Fools today is: How seriously should we take Iran's threat to both the world's peace in general and its crude oil flows in particular? My best assessment of this situation is that, with its vital geographic location, its financial back to the wall, and its significant position within OPEC, Iran should be taken very, very seriously.   

On that basis, I would continue to urge Fools to carefully monitor these emerging geopolitical strains and to retain international energy representation in their portfolios. My two absolute favorites are ExxonMobil and service giant Schlumberger (NYSE:SLB).

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Fool contributor David Lee Smith does own shares in Schlumberger, but not in the other companies mentioned. He welcomes your questions or comments. The Fool has a disclosure policy.