By Michael Jones, Scott Vincent

March 28 - (The Insurer) - WR Berkley's shares have risen more than 10% in early trading following this morning's announcement that Japanese carrier Mitsui Sumitomo Insurance is to purchase 15% of its outstanding common stock.

All common stock will be purchased through open market or private block purchases, MSI said in a statement on Friday. It added that the Berkley family will not be selling any of its common stock, nor will MSI purchase common stock from WR Berkley.

MSI said its purchases of WR Berkley common stock from third parties will be made "over a reasonable time period". It added that it cannot acquire 10% or more of the outstanding common stock without certain regulatory approvals.

MSI said that WR Berkley's current market cap is $25.1 billion, with 15% of that equating to approximately $3.8 billion.

The Japanese insurer said that once it has acquired 4.9% of WR Berkley's outstanding common stock, it has agreed to vote all of its WR Berkley common stock pursuant to recommendations of the family, except in limited circumstances.

MSI is expected to nominate a designee for the WR Berkley board by March 2026 and expects to complete the acquisition by this point.

The MS&AD subsidiary said it hopes to benefit from the strengths of WR Berkley in the U.S. market, including its strong earnings and growth.

It said this will help diversify its portfolio and risks, strengthen its earnings and raise its capital efficiency.

KBW analyst Meyer Shields had earlier predicted that WR Berkley’s shares would trade up following the announcement.

Shields said WR Berkley is expected to leverage an expanding relationship with MSI to expand its global footprint over time.

"MSI has agreed to customary standstill restrictions, likely precluding a fuller takeover," he said.