You wouldn't know it by looking at share prices in the sector, but certain oil-tanker rates have exploded in recent weeks.

Remember our discussion of how DryShips' (NASDAQ:DRYS) scary-high profits are closely tied to the Baltic Panamax Index? Well, for the crude-oil shippers, it's useful to keep an eye on the Baltic Dirty Tanker Index (BDTI). "Dirty" tankers transport crude, while "clean" tankers move refined products like gasoline or jet fuel. The two are generally not interchangeable, because crude's sludgy residue would contaminate other products.

In the last two weeks of November, the BDTI, which tracks a dozen different tanker routes, rose more than 50%. Long-haul voyage rates have changed even more dramatically in the same period. While owners of very large crude carriers (VLCCs) were reluctantly accepting jobs in the vicinity of $17,000 a day -- actually a money-losing proposition for a company such as Frontline (NYSE:FRO) -- benchmark rates have recently risen to as high as $140,000 a day.

Let's return to those relatively stagnant share prices. If tanker operators are now able to earn multiples of what they were pulling down just two weeks ago, why haven't their stocks rocketed higher?

For one thing, many of the bigger companies in this space, such as Overseas Shipholding Group (NYSE:OSG) and Tsakos Energy Navigation (NYSE:TNP), have a mix of crude and product carriers in their fleet.

Second, tankers come in all shapes and sizes, so even pure crude-movers don't necessarily have the type of transporter that's most in demand. Nordic American Tanker (NYSE:NAT), for example, owns only Suezmax vessels, which are smaller than VLCCs and thus don't make the same long-haul voyages.

Third, even Knightsbridge Tankers (NASDAQ:VLCCF), a rarity among publicly traded shippers in that its fleet consists solely of VLCCs, has only two vessels trading on the spot market.

I'm afraid those of you looking to make a quick buck on this turning of the tanker tide are straight out of luck. But if you're a shareholder of a company such as OSG or Teekay (NYSE:TK), you have to be pleased that the stormy scenarios causing analyst agitation have simply not taken shape.

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Fool contributor Toby Shute doesn't have a position in any company mentioned. The Motley Fool has a tranquil disclosure policy.