Transocean, the operator of the Deepwater Horizon oil drilling rig that exploded in the Gulf of Mexico in April, is considered a world leader at the complex and risky business of deep water drilling. That's to be expected from a global company that is the world's largest offshore drilling company.

But recent reports reveal that deepwater drilling is not the only area of expertise for Transocean — the other is tax avoidance.

An article in the New York Times earlier this month reported that the company is, and has been, under investigation by authorities in Norway, Brazil and the United States for a range of questionable business practices.

In the U.S., the Securities and Exchange Commission is looking into some Transocean equipment that was forwarded through Iran, and also its business dealings with Syria. Doing business with those countries, which are accused of sponsoring terrorism, is illegal.

Transocean is also under investigation in the U.S. for its actions in trying to avoid liabilities in a pollution case in Louisiana.

Even more significant, in terms of a pattern of behavior, are suggestions that the company is abusing U.S. tax laws through its corporate base in Switzerland. Most of its executives still are based in Houston, Texas.

The company's history is revealing. It moved its headquarters to the Cayman Islands from Houston in 1999 for tax reasons. After some corporate acquisitions, according to the Times report, the company then moved its headquarters, again for tax reasons, to Switzerland from the Cayman Islands.

One remarkable story seems to say a lot about how far the company will go to play tax- avoidance games. The Times reported that while moving a large floating oil-rig platform from a repair yard in Norway, the company diverted the towed rig into British waters in the North Sea. While it was temporarily there, the company transferred ownership of the rig between two Transocean subsidiaries, and later argued that after the rig was producing oil in the North Sea, it did not have to pay taxes to Norway on its profits because of the transfer.

These reports suggest the company might have nearly as many international lawyers and accountants specializing in tax matters as it has geologists and deep-water-drilling engineers.

No doubt, large global companies such as Transocean are routinely being watched or investigated by a variety of governments or agencies because their operations are so complex. But Transocean appears to have a disturbing track record when it comes to the lengths it will go to avoid paying its fair share of taxes — to the United States Treasury or to other countries.

Now that it is under intense scrutiny, more evidence of suspicious activity might come to light. Transocean should be forced to pay all the appropriate taxes and penalties that it owes. And this story might also shine light on other companies actively working to avoid taxes by exploiting legal loopholes, and even engaging in illegal maneuvers.

The United States should go after Transocean and all other companies going to these lengths to avoid paying taxes owed to the U.S. Treasury. In addition, taxpayers should demand that Congress work to close the abusive tax loopholes while also directing the Internal Revenue Service and other agencies to pursue tax cheats, no matter where they are found and no matter how large and influential they might be.

The BP oil leak was caused by technical and human failures. But additional failures are being discovered, not only in oil drilling safeguards, but also in regulatory and financial areas, both of which demand serious reforms.