Although rates for property reinsurance remained generally stable at the Jan. 1 renewal, rates for marine business rose sharply, according to a study by Willis Re, the reinsurance arm of London-based brokerage Willis Group Holdings P.L.C.

According to the study, released Monday, U.S. rates for property catastrophe business were flat or down by 5%, on average, on loss-free accounts. Accounts that suffered losses in 2012 saw rate increases of up to 10%, according to the report.

A number of large accounts that suffered losses from Superstorm Sandy do not renew until later in the year, the report noted.

For international property catastrophe business, rates were flat or down by as much as 5%, on average, the report said.

“In the absence of Superstorm Sandy, reinsurers would have found it difficult to resist buyer pressure for further concessions,” said Peter Hearn, chairman of Willis Re, and John Cavanagh, CEO of Willis Re, in the report. “As such, Sandy's impact has helped to stabilize market pricing on an overall basis, and reinsurers have largely delivered to their clients in terms of capacity and continuity,” they said.

Marine reinsurance buyers are seeing rate increases of 15% and higher even on loss-free offshore energy excess-of-loss contracts after a “difficult year” for the marine market, which suffered losses from Superstorm Sandy, the loss of the cruise ship Costa Concordia in January 2012 and a deterioration in losses stemming from the October 2011 M.V. Rena oil spill off the coast of New Zealand, among other things, according to the report.

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Many marine insurance buyers have increased their retentions to help offset the impact of rate increases, the report noted.

Renewals for marine business were very late, partly because of uncertainty over Superstorm Sandy losses, according to the report.

Rates for marine insurance buyers that are members of Protection and Indemnity Clubs are likely to see rate increases of a minimum of 10% when that business renews on Feb. 20, with the reinsurance program purchased by the International Group of P&I Clubs subject to a rate hike of more than 40%, according to the report.

The report is available here.