By Scott Malone

BOSTON (Reuters) - A group of investors including
the two largest U.S. public pension funds asked 27 top oil and
gas companies Thursday to disclose what they have done to
make their offshore drilling safer in the wake of the BP
oil spill.

Members of the Ceres coalition of socially-concerned
investors, who manage some $2.5 trillion in assets, called on
companies including Exxon Mobil Corp and Chevron Corp
to say what steps they are taking to make sure their
offshore operations are not vulnerable to the sort of failure
that caused the April 20 blowout, which triggered the world's
worst accidental marine spill.

"The shareholder harm that has flowed from the BP spill has
focused investor attention on governance, compliance and
management systems needed to minimize risks associated with
deep water offshore oil and gas development worldwide," the
investors, who included top financial officials of California
and New York State wrote.

BP's market value has fallen more than a third since the
blast on the Deepwater Horizon rig in the Gulf of Mexico that
set off the disaster, and the company is in the process of
selling some $30 billion in assets to cover the cost of the
cleanup.

"Investors have a right to full disclosure of the risks
associated with oil companies' offshore operations," said Bill
Lockyer, California's treasurer and a trustee of pension funds
Calpers and Calstrs, which saw the value of their BP shares
fall $349 million after the spill.

The letter, also sent to Royal Dutch Shell Plc and
Petrobras, asks the companies to disclose how much
they have invested in developing safer drilling techniques and
how the companies evaluate the safety standards of the
contractors they hire to run drilling operations.

A group sent a separate letter to 26 global insurance
companies including American International Group,
Lloyd's of London and Swiss Re, asking if
they planned to limit their future exposure to offshore
drilling operations.

BP on Wednesday said it had stemmed the flow of crude from
the well by pumping in heavy drilling mud, some 107 days after
the leak. That news followed several less successful attempts
to cap or plug the well.

"Would I invest in an offshore drilling company if its
disclosure statement revealed that its 'rapid response' to a
catastrophic oil spill involved the unproven technique of
stuffing golf balls, hair clippings and shredded tires down a
well? Probably not," said Pennsylvania State Treasurer Rob
McCord, who also signed the letter.
(Reporting by Scott Malone, editing by Dave Zimmerman)