Brazil's environmental regulator on Friday denied French oil giant Total a license to drill for crude in five blocks near the mouth of the Amazon river.
Regulatory agency Ibama said the license was denied "due to a set of technical problems" identified during the application process.
It explained that the decision was based "on the deep uncertainties" detected in an emergency plan presented, "aggravated by the possibility of an oil spill that may affect the coral reef present in the region and by extension marine biodiversity."
A Brazilian prosecutor warned of "extreme environmental peril" in recommending against the granting of the drilling license earlier this year, saying that: "the only way to guarantee avoiding environmental damage to the area is to deny the license."
Environmental campaigners Greenpeace meanwhile warned that a previously discovered coral reef had been found to extend right into where Total plans to drill.
The finding, made during a research expedition, invalidated Total's environmental impact assessment, which was based on the reefs being located at least five miles (eight kilometers) from drilling, Greenpeace said.
In 2013, Total joined BP and Brazil's Petrobras to buy the exploration blocks near the mouth of the Amazon. But they had yet to win permission to search.