This match is live on BBC One tonight with build-up starting at 18:20 GMT.false
It is also on BBC Radio 5 Live and coverage has already started on there.
And you can see/hear both on this very page.
Post update
Argentina v Australia (19:00 GMT)
The Sydney Opera House has been lit up in the Socceroos colours for tonight's game. It will be 6am local time at kick-off.
EPACopyright: EPA
'Romero over Martinez in Argentina's back line'
Argentina v Australia (19:00 GMT)
Pablo Zabaleta
Ex-Man City and Argentina defender on BBC Radio 5 Live
Lisandro Martinez is playing in the Premier League and I think he's been a great signing for Manchester United. I know he's not the tallest but he is still strong in the air and he is aggressive and I don't see him being a problem for any of those games.
It seems like for Scaloni, Romero brings him something more on set pieces than Martinez so that has been a discussion, who will play for Argentina at the back.
Who awaits the winners?
Argentina v Australia (19:00 GMT)
Whoever wins this game will face the Netherlands on Friday (19:00 GMT) in Lusail for a place in the semi-final of the World Cup.
The Dutch beat the USA 3-1 a couple of hours ago.
Post update
Argentina v Australia (19:00 GMT)
Andy Cryer
BBC Sport in Qatar
If the metro was like this three and a half hours before kick-off what will it be like later? Especially if Argentina win...
Could this be the final time we see Lionel Messi at a World Cup?
Australia have never been to the quarter-finals before - but win today and they will be there - and Messi's bid to win a World Cup before retiring will surely be over.
Welcome to live text, TV and radio coverage of the second knockout game of the Qatar World Cup.
Live Reporting
Emlyn Begley
All times stated are UK
How to take a World Cup penalty
In case it goes that far tonight, here is a handy guide on how to take a World Cup penalty.
Post update
How to follow on the BBC
Argentina v Australia (19:00 GMT)
This match is live on BBC One tonight with build-up starting at 18:20 GMT.false
It is also on BBC Radio 5 Live and coverage has already started on there.
And you can see/hear both on this very page.
Post update
Argentina v Australia (19:00 GMT)
The Sydney Opera House has been lit up in the Socceroos colours for tonight's game. It will be 6am local time at kick-off.
'Romero over Martinez in Argentina's back line'
Argentina v Australia (19:00 GMT)
Pablo Zabaleta
Ex-Man City and Argentina defender on BBC Radio 5 Live
Lisandro Martinez is playing in the Premier League and I think he's been a great signing for Manchester United. I know he's not the tallest but he is still strong in the air and he is aggressive and I don't see him being a problem for any of those games.
It seems like for Scaloni, Romero brings him something more on set pieces than Martinez so that has been a discussion, who will play for Argentina at the back.
Who awaits the winners?
Argentina v Australia (19:00 GMT)
Whoever wins this game will face the Netherlands on Friday (19:00 GMT) in Lusail for a place in the semi-final of the World Cup.
The Dutch beat the USA 3-1 a couple of hours ago.
Post update
Argentina v Australia (19:00 GMT)
Andy Cryer
BBC Sport in Qatar
If the metro was like this three and a half hours before kick-off what will it be like later? Especially if Argentina win...
Team news - Messi plays 1,000 career game
Argentina v Australia (19:00 GMT)
Shamoon Hafez
BBC Sport at Ahmad bin Ali Stadium
Argentina make one changes from the side that beat Poland in the last group game.
Alejandro Gomez comes in for Angel di Maria.
Captain Lionel Messi makes his 1,000th career appearance - 169 for his country and 831 for Barcelona and PSG.
Argentina XI: Martinez, Molina, Romero, Otamendi, Acuna, De Paul, Fernandez, De Paul, Gomez, Alvarez, Messi.
Australia also make one change from the side that shocked Denmark to reach the knockout stage.
Keanu Baccus comes in for Craig Goodwin.
Stoke defender Harry Souttar starts at the back.
Australia XI: Ryan, Degenek, Souttar, Rowles, Behich, Leckie, Mooy, Irvine, Baccus, McGree, Duke.
Post update
Argentina v Australia (19:00 GMT)
Could this be the final time we see Lionel Messi at a World Cup?
Australia have never been to the quarter-finals before - but win today and they will be there - and Messi's bid to win a World Cup before retiring will surely be over.
Welcome to live text, TV and radio coverage of the second knockout game of the Qatar World Cup.