W. R. Berkley (WRB) said Friday that Mitsui Sumitomo Insurance has agreed to buy 15% of its stock through open market purchases or private transactions with third parties.

The Berkley Family and W.R. Berkley will not sell shares to Mitsui Sumitomo under the plan, the company said.

Under the agreements between Mitsui Sumitomo and the Berkley Family, once Mitsui Sumitomo acquires 4.9% of the outstanding shares, it agrees to vote those shares in accord with the recommendations of the Berkley Family, except in limited circumstances, the company said.

Once Mitsui Sumitomo acquires at least 12.5% of the outstanding shares, the Berkley Family agrees to recommend the nomination and election of a Mitsui Sumitomo director designee to the company's board, it said.