Despite the economic slowdown, there are still some growth businesses. Take manufacturing, for instance. No, not auto or widget making. I'm talking about the manufacturing of exchange-traded portfolios.

You've no doubt noted, in particular, that the number of exchange-traded notes and funds tracking the Oil market has ballooned. Which inevitably leads to questions on their performance. Especially in these credit-addled times, questions abound about exchange-traded notes.

So here's the quick-and-dirty. There are three long and two short notes. The original long note was the iPath DJ-AIG Crude Oil Total Return ETN (NYSE Arca: OIL). It's been around a couple of years and is an obligation of the U.K.'s Barclays Bank plc.

Then, with near-perfect timing, the PowerShares suite of oil notes was launched this summer, just in time to catch the swoon in oil prices. These notes, offering single and double exposure - short and long - to the Oil sector of the Deutsche Bank Liquid Commodity Index, are issued by the German bank's London branch.

Spot NYMEX oil has sunk 71.7% since the PowerShares notes' launch. Here's how the notes have responded:

OIL ETN Performance (7-Jul-08 through 17-Dec-08)

From the table, you can easily see the short notes have fared well. The interesting numbers, however, have to do with liquidity.

The spread between the bid and offer is typically the best indicator of liquidity. A tighter spread denotes a more liquid market. Clearly, the more mature OIL portfolio has the advantage over the OLO portfolio.

The levered notes, too, are more actively traded and more liquid. This most likely reflects the utility of these securities as hedging alternatives to futures as well as outright portfolio positions.

Also notable is the liquidity index reading for each note. The index is a volume-weighted metric that tells you the size of a trade - all else held equal - needed to move the note market one percentage point. The higher the number of notes, the more liquid the market.

Of course, all things aren't always held equal. The notes' market makers must track the underlying index with their bids and offers to keep arbitrage opportunities from opening up. You don't have that in regular old stocks.

But if you're trading oil ETNs, you probably think plain old stocks are boring, right?

OIL ETN Performance