Information Handling Services Incorporated, or IHS, claims that unlike other militant organisations, IS has secured its own stream of funding instead of having to rely on donors.
Understanding how IS makes and spends its money is playing a crucial role in the ongoing campaign to defeat the organisation.
Now a report based on data found on social media and other open sources appears to reveal some of the group's inner workings.
According to security analysis by IHS Global Strategies, in the later part of 2015 IS was earning about AU$110 million a month.
It says around half came from taxing people living in IS-controlled areas and from confiscated assets.
The group controls several areas in Syria and western Iraq, where they tax residents up to 20 per cent on basic services like electricity, mobile phone coverage and internet access.
But much of IS money - around 43 per cent - comes from oil.
Just who is buying the oil remains unclear.
In recent weeks, Russia has accused Turkish President Recep Tayyip Erdogan and his family of directly benefiting from the illegal smuggling of oil from IS-held territories.
Now Iraq's Prime Minister, Haider al-Abadi, while not accusing Turkey's president, also says Turkey is the main conduit for IS oil-smuggling operations.
"We hope for international support to prevent terrorists entering Syria and Iraq and to stop Daesh smuggling of petrol among other things, including Iraqi antiquities. Most of this smuggling - including that of terrorists, frankly - happens via Turkey."
But the IHS report also notes that airstrikes have significantly degraded IS's ability to both refine and transport oil.
It says the group is still producing oil but Turkish efforts to stop the smuggling and several battlefield defeats mean IS has been forced to rely on local markets in Syria and Iraq.
US jets have targeted and destroyed several hundred oil-smuggling trucks in recent weeks.
And the operations have proven to be effective, according to the Chairman of the United States Joint Chiefs of Staff, Joseph Dunford.
"We've seen a significant increase in the tempo of our strikes over the past couple of weeks. We estimate that approximately 43 per cent of the revenue stream ISIL derives from oil has been affected over the past 30 days."
But questions remain over why it took the US so long to target the trucks specifically.
US state department spokesman John Kirby says while the focus has always been on finding ways to cut off IS revenue streams, several other factors need to be considered as well.
"It's not like we've never been focused on their oil revenue, it's something we've constantly focused on. That's one. Number two, when you do that, just like every other set of targets you try to strike, you have to be mindful of collateral damage, you have to be mindful of the infrastructure you're hitting and the degree in which it should be or should not be preserved, and I think the third piece I'd say to answer your question is this is a very dynamic, fluid situation. This is an adaptive enemy, he's agile and very determined. We have to be agile and adaptive as well, and we are."
Mr Kirby once again dismissed Russia's accusations that the Turkish government is profiting from IS oil smuggling.
But Richard Becker, from the protest group the Answer Coalition, has told Russia Today that the US appears reluctant to discuss its relationship with Turkey in detail.
"These are not small-scale operations that are being carried out, these aren't smugglers with donkeys going over mountain passes or anything like that. This is a huge operation that's going on. The United States is very protective about its relationship with Turkey, but at the same time in recent weeks it's become more apparent that this is going on and the United States claims it's fighting ISIS."
While IS has managed to secure a steady stream of funding, the IHS report says there is evidence of financial strain.
The security firm's conflict monitor shows IS is spending almost as much as it's making, and there are reports it is cutting fighters' salaries and introducing new agricultural taxes.
This report comes just months after an investigation by the Financial Times claimed IS made over two million dollars a day from oil.
While credible, the investigations' results are almost impossible to verify.
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