The outstanding market for collateralized reinsurance sidecar structures has continued to grow at pace thanks to investor interest in the structures, with the latest estimate from Aon Securities putting invested capital in sidecar vehicles at a new high of $19.6 billion.
Aon’s latest estimate shows growth in both property and casualty reinsurance sidecars in the second-half of 2025, resulting in a new record size for the collateralized sidecar marketplace.
Previously, Aon Securities data shows that reinsurance sidecars reached a new record high of $17 billion as of June 30th 2025, representing around 70% expansion of this segment of the ILS market in just one year.
That was up from a previous estimate for outstanding reinsurance sidecar capital having reached $10 billion at the middle of 2024.
Now, with the latest data on the reinsurance sidecar market from the broker being as of September 30th 2025, it appears this ILS market segment has expanded its invested capital base a further 15% in just the third-quarter of the year.
Aon stated that 2025 saw, “A proliferation of sidecar structures, as investors’ desire to get closer to underlying insurance risk was matched by sponsors’ desire to earn valuable fee income.
“Unlike in prior years, many of the new vehicles are being set up to support longer-tailed casualty risk. Sidecars have also been formed to support MGA business and even legacy transactions.”
The latest estimate, as of the end of Q3 2025, is for property reinsurance sidecars to have reached $17.9 billion of invested capital, while the relatively newer casualty reinsurance sidecar segment has now reached $1.7 billion.
Giving total reinsurance sidecar invested capital of $19.6 billion as of September 30th 2025.
We expect the figure will stand at more than $20 billion at this time, given there has been additional sidecar activity around the end of year reinsurance renewals.
Aon further commented on the sidecar segments outstanding growth, “The sidecar market also continued to grow in 2025 through new (re)insurers, new investors and new structures with the property sidecar market at $17.9 billion of invested capital and the casualty sidecar market at $1.7 billion of invested capital.
“While the estimated $1.7 billion of sidecar investment into casualty is small relative to property, these structures give insurers and reinsurers more flexibility in an improving market. Recent investor interest in these transactions is due to higher interest rates and the growth in U.S. private credit platforms and we expect more of these transactions needs to be plural executed in 2026.”
On the property sidecar segment Aon further explained, “The property sidecar market remained strong despite the passing of the current pricing cycle peak as investors remain interested in historically elevated rates. The selective addition of specialty risk to property portfolios also helped expand the value of coverage provided while increasing potential returns for investors.”
Aon also highlighted that sidecars are increasingly becoming “a mainstream option for clients and investors which invest premium float in attractive assets, including private credit, to match the corresponding liability profile.”
Adding that, “(Re)insurance portfolios ranging in content from solely casualty to multiline property and casualty used this evolution of traditional long-tail asset-liability matching.”
Aon anticipates the growth trend in reinsurance sidecars will continue, as investors and sponsors continue to find alignment and utility on both sides of the trade.
“We believe that the growing value of new reinsurance capacity, enhanced ceding commissions and partnerships with skilled asset managers will encourage more clients to pursue sidecars in 2026,” the broker stated.
The expansion of the reinsurance sidecar market over the last two years has been particularly significant, with the invested capital in the sector having nearly doubled since the mid-point of 2024.
Prior to that, the reinsurance sidecar market had reached around $8.4 billion in capital outstanding back in 2015, then shrank back before beginning to resurge again for the 2024 underwriting year.
Find details of numerous reinsurance sidecar investments and transactions in our directory of collateralized reinsurance sidecars transactions.
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