The operations highlight comes about 15 years after Athabasca first began operations in 2003.
Canadian Natural president Tim McKay said the billionth barrel is a demonstration of the size and scale of the oil sands mining operations of Canada.
"The oil sands, through responsible development, provide sustainable long-life, low-decline production and significant value for stakeholders," he said.
"This milestone could not have been achieved without the dedication of the employees and contractors who focus on safe, reliable operations, while minimising our environmental footprint to ensure long-term sustainable development."
The Calgary-based senior producer acquired a 70% interest in Athabasca in March 2017. Owners holding the balance include Chevron Canada at 20% and Shell Canada with 10%; Canadian Natural purchased its interest from the latter.