WASHINGTON—Employees of a federal agency that regulates offshore drilling—including some whose duties included inspecting offshore oil rigs—accepted sporting-event tickets, meals, and other gifts from oil and natural-gas companies and used government computers to view pornography, according to a new report by the Interior Department's inspector general.

The report—published Tuesday on the inspector general's website—describes a culture in which inspectors assigned to the Lake Charles, La., office of the Minerals Management...