Trade credit owed by Australian businesses is estimated to have been more than $80 billion at March 2013, which accounted for around eight per cent of total liabilities of all businesses, the RBA says in an article in its latest Bulletin.The RBA sourced the estimate from the Dun & Bradstreet's financial database, which compiles data on unlisted businesses.The RBA said the D&B data "suggests that trade credit is a particularly important source of debt funding for the smaller segment of the business sector and accounted for around 40 per cent of their total liabilities."The RBA said the use of trade credit within the unlisted sector "increases with business size until the firm reaches a size of 50 to 199 employees. For unlisted businesses larger than this, there is typically little increase in the use of trade credit relative to assets [which] may reflect the tendency for unlisted businesses to gain more access to other forms of funding once they reach a certain size."Modelling by the RBA confirmed that "the Australian unlisted business sector is likely to be treating trade and bank credit as partial substitutes."