Editor's note: An earlier version of this story incorrectly reported the insurance coverage that Japan's Mitsui had. This corrected version of the story reflects the change in the sixth paragraph.

NEW YORK—Though the Deepwater Horizon disaster in the Gulf of Mexico is not estimated to be a major property/casualty insurance event, risk management consulting firm Towers Watson & Co. estimates commercially insured losses will range between $4 billion and $6 billion.

Towers Watson released its estimate Monday, adding that the insured losses are just a slice of the economic loss suffered in the Gulf since the oil rig's April 20 explosion and subsequent spill. So far, total losses in the Gulf are estimated to be $35 billion.

“Usually, a major event causes the market to turn, with prices rising in the wake of red ink,” said James Hole, managing director within New York-based Towers Watson's reinsurance brokerage, in a statement. “We do not expect that Deepwater is a sufficiently significant event to turn the overall commercial insurance market.”

Transocean Ltd., owner of the drilling rig, disclosed that it has a total of $945 million of insurance coverage on it, Towers Watson said. Of that total, $560 million is insured property value, while $385 million is additional coverages to pay for mitigation and recovery efforts.

Transocean also disclosed it has $950 million of liability insurance coverage.

BP P.L.C., Anadarko Petroleum Corp. and Mitsui & Co. Ltd.—all in a joint venture as operators of the well—disclosed their insurance coverage to Towers Watson. Canada's Anadarko has $163 million in insurance coverage to draw upon; Japan's Mitsui disclosed it has pollution liability insurance coverage of $45 million; and London-based BP has no commercial liability insurance coverage but has its own captive insurer, Jupiter Insurance Ltd.

It was reported Tuesday that Mitsui, which holds a 10% stake in the now-capped well through its Mitsui Oil Exploration Co. Ltd. unit, has received a $480 million bill from BP as part of cleanup costs from the oil leak.

Anadarko has a 25% stake in the well, while BP has the remaining 65%.

Meanwhile, Towers Watson reported that Cameron International Corp., the manufacturer of the well's blowout prevention mechanism, disclosed it has $500 million in liability coverage; and Halliburton Co., responsible for cementing the well, disclosed it has $600 million of liability coverage.

The total coverage limits for all involved is $3.3 billion, Towers Watson said, and there still is the possibility that other companies may be drawn into litigation. Towers Watson noted directors and officers liability and workers compensation losses may add to the tally.