Income Tax Assessment Act 1997
The *capital proceeds from a *CGT event are increased if another entity *acquires the *CGT asset (the subject of the event) subject to a liability by way of security over the asset.
They are increased by the amount of the liability the other entity assumes.
You sell land for $150,000. You receive $50,000 (the capital proceeds) and the buyer becomes responsible for a $100,000 liability under an outstanding mortgage. The capital proceeds are increased by $100,000 to $150,000.