The probe focuses on agreements for joint reinsurance and sharing of insurance claims between so-called Protection and Indemnity Clubs run by shipowners to manage their insurance affairs.
The European Commission, the EU's executive agency, said it wants to determine whether agreements between the 13 members of the International Group of P&I Clubs reduce competition between the clubs and "restrict, to a certain extent, the access of commercial insurers and/or other mutual P&I insurers to the relevant markets."
The International Group jointly insures about 93 per cent of the world's ocean-going tonnage, according to the Commission.
The Commission said the P&I agreements are not automatically covered by the EU's anti-trust exemption for the insurance industry which came into force in April because their market share is well above the qualifying 20-25 percent ceiling laid down in EU competition regulations.
The investigation follows the expiry in 2009 of the second 10-year anti-trust exemption for P&I Clubs.
The International Club said it expects the Commission will renew anti-trust exemption as there have been no relevant or material changes to the P&I arrangements or in the market since 1999 when it concluded there were no competition concerns.
The Commission said it opened the investigation on its own initiative and has not received any complaints about P&I Club practices.