If you're catching up on the oil market this morning, you might be confused to read that prices are both at $100 and $107. Which is right?

Both, and the fact that two very different prices are floating around shows how nervous oil traders are getting about supplies after President Trump rejected an Iranian proposal that would reopen the Strait of Hormuz.

-- The higher price is for contracts that will deliver Brent crude oil in November. That's the soonest you can get your hands on the crude via a futures contract. The contracts expire at the end of this month.

-- The lower price is for contracts that expire in October, and cover oil that will be delivered in December.

Normally, the gap between prices for two consecutive monthly contracts is small-a couple of dollars at most. When oil markets are either in feast or famine, it can widen dramatically, especially when contracts approach expiration.

In this case, the earlier, November contract is more than $7 a barrel above the December contract, signaling a scramble to get hold of oil as soon as possible. In trader jargon, that setup is known as "backwardation".

The opposite, called "contango", takes place when there's a glut and means soon-to-expire contracts are cheaper.