DiNapoli, as trustee of the state's $133-billion public employee pension fund, claims the British oil giant misled investors about the safety of its operations.
BP's stock value dropped roughly in half following the April 20 oil rig explosion and spill.
The New York retirement fund for public workers held about 19 million shares.
BP's stock price Wednesday closed down 16 cents, or 36 percent, to $43.95.
Meanwhile, eight months after the spill, BP's costs look manageable.
As the Gulf oil spill gushed out of control, BP's financial liabilities seemed big enough to sink the company. No more.
Cleanup, government fines, lawsuits, legal fees and damage claims will likely exceed the $40 billion that BP has publicly estimated, according to an Associated Press analysis. But they'll be far below the highest estimates made over the summer by legal experts and prominent Wall Street banks, such as Goldman Sachs, which said costs could near $200 billion.