The sale was of surplus gas, which came from Alinta's pipeline that supplies its 502 megawatt Braemar power station near key CSG fields in southern Queensland.

The transaction, with the buyer unrevealed, took place within 15 minutes of the hub opening trade for the first time on March 20.

Overall there were six trades on this day for small volumes of gas, with the day's trade worth $25,800.

An AEMO spokesperson said it was an "encouraging start" for the hub.

Its official launch is expected this Wednesday.

Following recommendations from the Standing Council on Energy and Resources, AEMO was tasked with developing the hub "to enhance transparency and reliability of gas supply by creating a voluntary market that offers a low-cost, flexible method to buy and sell gas at interconnecting transmission pipelines".