The discovery was made at the Lagoa Bonita field at well 3BRSA881DES.
Petrobras is using the Drillfor-8 rig on the well, which is due to be drilled to a final depth of 2,200m, according to a separate ANP filing.
Last week, Petrobras reported two new oil and natural gas discoveries onshore Brazil's Potiguar basin.
The first discovery was made on block BT-POT-8 at well 3BRSA859DRN. The second find was made on nearby block BT-POT-9 at well 3BRSA893RN.
Companies are obligated to inform ANP of any potential oil discoveries. The routine notifications are not an indication of potential reserves or if commerciality could ever be declared.