BHP Billiton has revealed the true extent of its sweetheart deal with tax authorities in Singapore and acknowledged that the Australian Tax Office is chasing it for $500 million in unpaid taxes and fines in relation to the so-called "Singapore sling".

The global miner, once referred to as "the big Australian", is paying an effective tax rate of just 0.002% - effectively zero - on the hundreds of billions of dollars in sales of Australian resources it directs through its Singapore "marketing hub".

The ATO says BHP Billiton owes $500 million in unpaid taxes and fines. Credit:Ross Swanborough

Between 2006 and 2014, the company booked profits of $US5.7 billion in Singapore, it said in a statement to the Senate inquiry into corporate tax avoidance. BHP executives refused to answer the same questions when they appeared at recent public hearings, citing commercial confidentiality.

The company said it paid just $US121,000 in tax in Singapore – a paltry $US15,000 a year – after striking a special deal with the trade-friendly Asian nation to locate its marketing arm there.