The company said live oil in the drilling mud was observed from three separate levels between 1708m and 1743m in sands described as having poor porosity. Anomalous gas readings were also recorded at these levels.
No hydrocarbon shows were recorded in good quality sands of the Precipice Sandstone target zone at around 1400m.
Managing director Barry Smith said the reservoir sands appeared to be poorer quality than expected but the occurrence of oil confirmed the Willaroo area had access to hydrocarbons generated from deeper source rocks.
"Further technical work, involving the acquisition and interpretation of wireline log data, needs to be done before we know the significance of this oil," he said.
"But its very existence has proved that a petroleum system operates in the southern region of the Bowen Basin, thereby upgrading other petroleum prospects identified in Orion's NSW licences in this basin."
Willaroo-1 is the first well in Orion's exploration program in NSW and is targeting 40 million barrels of in-place oil resources in the Jurassic sands and 115 billion cubic feet of gas in-place in the Permian sands.
The Willaroo prospect is immediately north of proven gas reserves near Narrabri in NSW.
Following Willaroo-1, the company's next well is planned to be Nyngynderry-1 in the Darling Basin in northwestern NSW.