The company that owned the oil rig that exploded in the Gulf of Mexico in April had widespread safety concerns about several of its other rigs in the gulf, and a month before the disaster it commissioned a broad review of the safety culture of the company’s North American operations, according to confidential internal reports.

In response to “a series of serious accidents and near-hits within the global organization,” Transocean, the world’s largest offshore drilling company, commissioned the risk management company Lloyd’s Register to investigate its Houston headquarters and three other gulf rigs besides the Deepwater Horizon to assess its safety culture.

The confidential internal reports, obtained by The New York Times, offer an unusually candid view of safety and maintenance concerns within the world’s largest offshore drilling company, and they indicate that the problems highlighted in earlier reports provided to The Times about the Deepwater Horizon were not limited to that rig, which exploded on April 20, leading to an oil spill that is estimated to have poured at least four million barrels of oil into the gulf.

Transocean has 14 rigs now operating in the Gulf of Mexico, and 139 worldwide, and these documents raise concerns about locations beyond Deepwater Horizon, especially the three additional gulf rigs that were recently investigated. In fact, one of those rigs is being leased by BP to drill one of the two relief wells near the Deepwater Horizon site.