It was a depressing conclusion to a summit from which, frankly, we expected little to be achieved on the crucial issue of Syria.
In a series of press conferences immediately afterwards, the stark differences between Russian President Vladimir Putin and his major Western counterparts were laid bare for all to see.
According to US President Barack Obama, a majority of leaders at the G20 summit were "comfortable" with his conclusion that the Syrian regime used chemical weapons on August 21.
But Putin still insists that it was rebel forces who used poisonous gases on that day, as a "provocation" to lure in foreign military intervention. In this conviction, the Russian leader would appear to be in a minority.
On the other hand, Obama is clearly failing to build a broad international coalition in favour of military action that may not necessarily have the support of the UN Security Council.
For and against strike action
It's true that the United States did succeed in getting 10 other countries at St Petersburg to sign a declaration which strongly condemns the use of chemical weapons, that says "the evidence clearly points to the Syrian government being responsible for the attack", and calls for "a strong international response".
But that is not quite the same as explicitly endorsing military action.
The countries who signed this statement are the US, the UK, France, Spain, Italy, Turkey, Saudi Arabia, South Korea, Japan, Australia and Canada. (The most surprising omission is Germany, and I'm hearing some suggest that German Chancellor Angela Merkel's decision was influenced by the imminent election in that country).
President Putin had already listed the countries who agreed with him on the dangers of military action in Syria. These were, he said, South Africa (apparently passionately so), Indonesia, Brazil, China, India, Argentina and Italy, (yes, I know, Italy has somehow been claimed by rival camps. I would love to know how this happened, and how this is playing out in Rome).
In other words, a sizeable chunk of the world's population is against Obama. And, as Putin was eager to remind us, even in the countries where leaders do support military action, there's little popular support for an attack on Syria, as poor old David Cameron, the British prime minister, has already found out to his cost. The UN Secretary-General Ban Ki-moon and Pope Francis have also spoken out against the use of force.
The compelling argument of those who don't want Obama to launch an attack is that only the UN Security Council can confer legitimacy on such an act, and if we ignore the Security Council, we will live in a lawless and increasingly dangerous world.
President Obama has an answer to that. He says he would prefer to go via the Security Council, but that body has proven itself to be paralysed.
It has become a place where international law is blocked, not enforced. He says that in the face of an appalling atrocity he is the one willing to take action to make our world a safer place.
This is a complex debate, and every course of action, and inaction, is fraught with possible dangers. And yet at St Petersburg, Obama often looked like a man who had at least half his mind on the domestic scene.
He has to convince his own electorate of the wisdom of what he's doing. He knows that the coming vote in the US Congress will go a long way towards defining his presidency.
PS - I thought this article in the Washington Post is a thought-provoking read on some of the horrible dilemmas in this debate - and looking at the accompanying map showing the handful of countries that have not signed the international accord against the use of chemical weapons, how do Angola, South Sudan (although maybe they've not had time since their recent independence) Egypt, Syria and North Korea justify their stance?
Follow Barnaby Phillips on Twitter at @BarnabyPhillips.