WASHINGTON—BP Products North America Inc., a unit of BP P.L.C., will pay a record $50.6 million penalty and submit to an “unprecedented level of oversight” to settle citations that followed a 2005 Texas refinery explosion that killed 15 workers, the U.S. Labor Department said Thursday.

The blast at BP’s Texas City, Texas, refinery injured 170 others at the plant and led to “failure to abate” violations stemming from a follow-up inspection last year that resulted in the $50.6 million in penalties. The amount is the largest fine ever issued by the Occupational Safety and Health Administration and paid by an employer, the Labor Department said.

“The size of the penalty rightly reflects BP’s disregard for workplace safety and shows that we will enforce the law so workers can return home safe at the end of their day,” the Labor Department said in a statement. “Additionally, the agreement provides an unprecedented level of oversight of BP’s safety program including regular meetings with OSHA, frequent site inspections and the submission of quarterly reports for the agency’s review.”

In a statement, BP said the agreement resolves 270 of 709 citations. BP also said it contested the citations and maintains that it has implemented safety enhancements at the refinery since 2005.

“BP and OSHA elected to focus on resolving 270 failure-to-abate citations, which are the subject of this settlement,” BP said. “Both parties have agreed to settle these matters and focus on moving forward collaboratively in order to continue to improve plant safety. This new agreement addresses the concerns that OSHA raised in these citations. BP is hopeful that this agreement will provide a platform to resolve the remaining citations.”

BP agreed to “quickly” address remaining concerns and hire independent experts to monitor its progress, the Labor Department said.