BBC: "Iranians will head to the polls on Friday to choose between the incumbent Mahmoud Ahmadinejad and three rivals. They are Mohsen Razai, Mehdi Karroubi and the man seen by most observers as main challenger, Mir Hossein Mousavi... If one candidate fails to win a 50% majority in Friday's vote there will be a run-off between the two front-runners a week later."
Renard Sexton says that "while the numbers have
been extremely variable between polls, and making a decision about what
polls to include or exclude from aggregating in a case like Iran is
nearly impossible, we can see a basic cycle that can be corroborated by
anecdotal news evidence over the last two months. The incumbent has
been largely held below a majority, which in the Iranian system is
significant for two reasons. First, an absolute majority is needed,
without which a runoff is certain. In addition, if Ahmadinejad fails to
earn a majority, he will be the first incumbent President running for
reelection to do this."