Despite the $20 billion settlement BP PLC struck with the U.S. Department of Justice over the 2010 Deepwater Horizon oil spill, tens of thousands of lawsuits could hit the courts this month, adding to the oil company’s ballooning costs.

About 85,000 individuals and businesses claiming nongovernmental economic damages tied to the spill are due to file lawsuits against BP by May 16. Their claims are separate from the $20 billion deal; most were either excluded from or opted out of a 2012 class action settlement that was supposed to resolve economic damages claims.