Where "Good Oil" Comes From
The most solidly documented account traces "the good oil" to Australian and New Zealand troops' slang in the First World War, where it meant reliable, welcome information — the sort worth passing on. The Australian War Memorial's Sir John Monash Centre lists it among the era's slang alongside furphy (a false rumour, named for the water carts soldiers swapped gossip around), plonk, and cobber. A separate, commonly repeated theory ties it instead to mining slang, where "striking oil" meant a genuine find — the two stories aren't necessarily contradictory, since "the real oil" as a figure of speech for solid information could plausibly have reinforced itself from both directions.
Whichever account is closer to the truth, the meaning has stayed stable for over a century: if someone's got "the good oil," it's information you can actually trust.
Source:
"What's the good oil on the new manager?"
How Aussies Actually Use It
You'll hear "good oil" most in workplace or social settings, when someone wants the real, reliable version of events rather than rumour or guesswork.
It pairs naturally with "what's" or "give me" — "what's the good oil" and "give me the good oil" are both extremely common ways to ask for it.
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