The deposit was discovered about 365 kilometers northwest of the oil-rich nation's coast through a drilling 1,100 meters deep, the Angola's National Agency for Oil, Gas and Biofuels (ANPG) said in a statement.
The ANPG added the new reservoir has physical properties "of high quality."
Angola -- which is one of the top two largest oil exporters of the black gold in Sub-Saharan Africa alongside Nigeria -- produces 1.2 million barrels a day, the country's mineral resource ministry told AFP.
The oil-dependent nation, which embarked on an ambitious reform program to diversify its economy, has faced strain from a decline in oil prices since 2014.
"ExxonMobil is optimising this resource and creating value for the Angolan people," president of ExxonMobil Upstream Company Liam Mallon said in the same statement.