NEW YORK (TheStreet) -- Shares of oil tanker companies, which ended trading Thursday mostly lower, have gone on a staggering run over the last two months.

Leading the pack has been Frontline ( FRO - Get Report), the largest publicly traded tanker company by market cap. Its shares have ripped higher by 42% since early February.

Shares of Frontline peer Overseas Shipholding ( OSG - Get Report) have risen in tandem, gaining about 20% over the same period, though it's been a rockier ride for OSG.

Shipping stocks in general are high-beta names, following the broader equities markets, but with an order of magnitude more intensity in either direction. With the Dow Jones Industrial Average breaking through 11,000, it's not entirely surprising that tanker stocks have risen to the degree they have. Further, many tanker stocks have heavy short interest, so whenever they experience a strong upside move, the squeeze is on.

But the bull run in the sector has both psychological and fundamental underpinnings. Shipping companies that specialize in moving crude across the oceans have benefited from rising rates for their services, buoyed by the recent run in the price of oil. The daily rate for a Very Large Crude Carrier, the biggest type of tanker ships in the world, has averaged about $50,000 a day in 2010. Late last year, some were predicting average rates for 2010 of $28,000 a day.

"All the bulls are coming out now," said Mike Reardon, vice president of research and marketing at Imarex, a clearinghouse of freight derivatives. "People were calling for Armageddon, and VLCC owners are out with champagne bottles right now."

Wall Street analysts have taken notice. Bears have turned into moderates. Moderates have morphed into bulls. And at least one bearish analyst, Martin Korsvold of the Norwegian investment house Pareto, flipped completely, upgrading the tanker sector last week. He lifted his rating on both Frontline and Overseas Shipholding's stock to buy from sell, writing, "The listed companies in our tanker universe are capitalized to weather choppy seas, hence the risk is on the upside."

Naysayers remain, however. And one such investor believes most stocks in the tankers sector are overbought, especially those companies who own no VLCCs, which is to say: every publicly traded tanker outfit except Frontline and Overseas Shipholding.

It's axiomatic in shipping that when rates move in either direction, the biggest ships experience the sharpest swings. And, indeed, during the latest upsurge, rates for smaller ships haven't kept pace with the rise among VLCCs. The most glaring example: Aframax-size vessels operating in the Caribbean, where the going rate on the spot market has plunged -- somewhat mysteriously -- to just $4,300 a day, well below their "op-ex" rate, which means these ships are hemorrhaging money.

Suezmax ships, meanwhile, have only increased 37% compared with a year ago. Compare that to VLCCs operating on Arabian Gulf-to-U.S. routes: spot rates for those vessels have more than sextupled since last year.

And, yet, shares of Nordic American Tanker ( NAT - Get Report) and Teekay ( TK - Get Report) have gained about 14% and 20%, respectively, since early February.

That's not nearly as sharp a rise as Frontline, of course, but it's enough to raise red flags for some.

"That's how you make money in shipping," the bearish investor said. "You buy when everyone hates it and short when everyone loves it. Right now, everyone loves it."

-- Written by Scott Eden in New York

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Scott Eden has covered business -- both large and small -- for more than a decade. Prior to joining, he worked as a features reporter for Dealmaker and Trader Monthly magazines. Before that, he wrote for the Chicago Reader, that city's weekly paper. Early in his career, he was a staff reporter at the Dow Jones News Service. His reporting has appeared in The Wall Street Journal, Men's Journal, the St. Petersburg (Fla.) Times, and the Believer magazine, among other publications. He's also the author of Touchdown Jesus (Simon & Schuster, 2005), a nonfiction book about Notre Dame football fans and the business and politics of big-time college sports. He has degrees from Notre Dame and Washington University in St. Louis.