ETA: The data is right,
but is incomplete data. See below.
Okay, so, historically, most of oil traded for US consumption is
not traded directly on the NYMEX; that's the spot market and while it does set the price, it's not the bulk of the oil - it's the tradable oil, and it's about 3%-5% of US consumption overall, which is to say, under 1M barrels/day.
That's historically, anyway. Check out trading volume over the last month and a half:

From Marketwatch.com's graphing toolsThat's original except for my highlighter-coloured adds (two arrows, some obvious text). The last day's volume on that chart is actually higher than shown in this view, the chart isn't complete for today yet, because volume data lags a bit.
We're seeing trading volumes that exceed total US consumption and continuing trading volumes twenty times normal in the face of rising prices. Now I can think of several things this
could mean, from day-traders swapping the same 1M barrels back and forth and back and forth (maybe this is one of the places those liquidity injections have gone) to demand destruction from contracted-delivery cancellation freeing more oil for the trading pits (but not that much, sorry - and particularly not in the face of
rising prices) to China moving in to buy oil off the US spot market directly (in which case, where's that oil coming from? US inventories have been falling sharply but not
that sharply) to significantly more dire interpretations. But really I just don't know.
But unless this data is wrong,
something is going on. A one-day error showing a massive volume pop I'd attribute to data error. But I can't do that for this many days in a row. So... what the hell?
ETA: Since I've had a few people raise the "it's just the end of the year" response (two in IM, one below): please note that this is a
two-year chart. This isn't normal end-of-year trading. For that, look at the tiny bip at the end of November '06 in this chart for comparison. That's how far down the rest of this chart has been compressed by this year's data.
If the data presented here is correct, this is very, very different.
ETA 2: Y'know what's even weirder?
Nobody else seems to chart this. At least, not the places I use, and not the places I found in Google that I can get to without being a subscriber. That means I can't validate (or invalidate) these numbers. It also means some other things. See comments (linked) below for details.
ETA 3: I got explorative with their URL parametre passing and was able to get data back to mid-2005, but no further. Nothing like this showed up EOY 2005, either - not even the little bump you get showing up EOY 2006. But that's throwing my own parametres at their graphing software so while I'm reasonably sure given everything that it's right, I'm less confident. Also, 26 December volume numbers are still being reported as 5 Mb, which is still crazytalk high, but if final is also a dramatic comedown from the previous month or so, which makes me ask
okay, why? Is somebody on vacation, or is somebody done setting something up?
ETA 4: This does not entirely jibe with what I have read previously (including yesterday),
but that could have been wrong or I could have misunderstood before. However, according to a commenter over on The Oil Drum, Marketwatch's charting, while accurate, only shows contracts expiring in a single month, which is to say in this case February, which makes their numbers look very strange. You have to have tools they don't offer to make volume numbers across all months appear in a chart. (And since theirs are the only tools I have that show it at all...) They also say that spot-market volume
has gone up dramatically in recent times, but not anything like this chart would have you believe. The part that doesn't line up is that I've read (from multiple sources) that the vast majority of actual pricing follows the NYMEX but is not actually traded on the NYMEX - that's where I get that 3% to 5% number - so if these are the actual volumes on a
monthly basis, that implies that most oil has actively moved to this market.