The U.S. Justice Department is conducting a criminal inquiry of nearly a dozen oil and oil-services companies, focusing on potentially illegal payments – bribes – to customs agents who provided freight forwarding and other services, including in Nigeria.

A civil investigation by the Securities and Exchange Commission also is under way.

Eleven US oil and oil-service firms have received a letter from the Justice Department’s criminal fraud section asking them to detail their relationship with Panalpina World Transport Holding Ltd., a Swiss-based shipping and logistics-management company.

The Justice Department letter, cited concerns about payments that may violate the U.S. Foreign Corrupt Practices Act.

According to the International Herald Tribune: “The Justice Department probe underscores the difficulty of complying with U.S. anti-bribery laws in countries that may be as awash in corruption as they are in oil”.