Brazilian oil giant Petrobras has admitted for the first time its series of exploration wells drilled in ultra-deep waters in the Campos basin have unlocked mostly natural gas and that developing them will be a challenge.

Over the past year, Petrobras has channelled exploration investments to the eastern portion of the Campos basin, a relatively uncharted frontier area within the wider Campos basin play, in search of hydrocarbons deposits.

Starting with the Naru probe in Block C-M-657, then advancing to Urissane in Block C-M-411, Yba in Block C-M-709 and finally Mairare in Block C-M-346, Petrobras has been notifying market regulator ANP it has found traces of hydrocarbons at all wells but failing to provide additional information.