Documents seen by Reuters show that IBAMA chief Rodrigo Agostinho warned in his decision against the "uncontrolled multiplication of future requests for environmental licenses" in the Foz do Amazonas basin, an oil frontier near the mouth of the Amazon River.

A decision by Brazil's environmental agency Ibama on Monday will allow state-run oil company Petrobras to take another step toward drilling for oil in a coveted offshore region, but it comes with a significant caveat for future permits in the area.

Documents seen by Reuters show that IBAMA chief Rodrigo Agostinho warned in his decision against the "uncontrolled multiplication of future requests for environmental licenses" in the Foz do Amazonas basin, an oil frontier near the mouth of the Amazon River.

The area, located in the northernmost part of Brazil's Equatorial Margin, is considered Petrobras' most promising oil frontier, as it shares geology with nearby Guyana, where Exxon Mobil is developing huge fields.

But Agostinho said it would be difficult to issue "piecemeal and successive exploration licenses" in the Foz do Amazonas basin without a complex environmental study known as AAAS, which could take years to complete.

IBAMA had previously requested an AAAS to evaluate Petrobras' bid, but Brazil's Attorney General issued a legal opinion stating that such a review should not prevent the granting of licenses.

Agostinho's new request increases uncertainty about future licenses in the region, where Brazil is preparing to offer new blocks at auction in June.

For now, the agency's head has approved a Petrobras proposal on how to assist local wildlife in the event of an oil spill in this environmentally sensitive region, which includes vast coral reefs and coastal indigenous communities.

Petrobras welcomed the decision on Monday, calling it a green light to test its environmental emergency plan, which it described as the last step before a final decision on granting the license.

The breakthrough for Petrobras represents a loss for IBAMA's technical staff, who had signed a document in February stating that the plan to rescue wildlife in the event of an oil spill had only a "remote chance" of success.

In 2023, IBAMA denied a Petrobras request to drill in the area, which the company immediately appealed, fueling divisions within the Brazilian government between environmental advocates and allies pushing for oil and gas development in the region.