Protection and indemnity (P&I) rates have risen by between 27% to 28% on average.
When Insurance Times went to press on Tuesday night, marine insurers were preparing to renew their reinsurance contracts.
The majority of them are members of international mutual P&I clubs, which enable better negotiating power.
The agreements were due to be signed on 20 February at noon.
A senior source who helped negotiate the terms of the renewal said the structure of the contract had not changed. But he added the pricing of reinsurance protection had altered.
He said: "The first $1bn (£700m) of cover is in two layers.
"Underwriters are paying 20% more premium for it than they did last year. The remaining two layers are facing substantial rate rises.
"But they are entirely consistent with the sort of price increases that all buyers of reinsurance have had to pay for all levels of cover."
The insider added rates for the last two layers have risen by up to 200% to 300% compared to last year. This makes the overall cost over the four layers an average of 27% to 28%.
The P&I contract is one of the latest, but most important renewals. It covers mainly marine liability, but also affects hull and cargo.
Last week, one ratings agency predicted P&I clubs would enjoy extremely favourable terms on the international group excess of loss reinsurance programme, because the terms were fixed last year until renewal in 2002.
Standard & Poor's Financial Services Group managing director Rowena Potter said: "It is clear that the majority of the clubs are seeking modest rate increases, in the 7.5% to 10% range".
