What: Shares of oil tanker company Nordic American Tanker Ltd. (NAT -2.51%) fell as much as 12% in early trading Monday after reporting fourth-quarter 2015 earnings. Shares settled to an 8% decline midday on Wall Street.

So what: Quarterly revenue jumped 80% to $77.4 million and the company swung from a $3.7 million loss a year ago to a $30.2 million profit, or $0.34 per share. That's impressive but analysts expected $86 million in revenue and earnings of $0.46 per share, which is why shares are down today.  

Tanker rates jumped from $24,000 per day a year ago to $39,800 per day in the fourth quarter, so operations are improving but they didn't line up with Wall Street's estimates. For today, that's a negative but it doesn't change the fact that fundamentals are improving rapidly.

Now what: The question for investors is more about how long the high dayrates will continue. Oil inventory is extremely high, but that probably won't last for more than a year or so and then we may go back to the low-margin environment seen the past few years because U.S. oil imports were falling. Shares look cheap today at eigjht times forward earnings estimates but watch for falling dayrates as international inventory drops and oil prices rise, which could both be bad for the tanker industry.