President Obama wants to slash fossil fuel subsidies in his new budget–and in his State of the Union Address, he called for cutting $ 4 billion in tax breaks and subsidies for oil companies. But how much in total subsidies do fossil energy companies get from the U.S. government?

According to this post from Scaling Green, coming up with an answer to that question is actually extremely difficult:

Energy trends analyst Chris Namovicz of the U.S. Energy Information Administration (EIA) was the latest speaker in our “Communicating Energy” lecture series. We took the opportunity to ask one of the top, neutral energy trends analysts in the country the question, “Do you know if someone has actually done a credible, comprehensive, definitive count of how much taxpayers underwrite fossil fuels in this country?” We added the thought that “there’s no one really widely available number where average citizens can say, yeah, this much of my money goes to pay ExxonMobil.”

According to Namovicz, there really isn’t such a widely available, definitive, comprehensive number.

Part of the problem is the complexity of the question. What’s a subsidy? Are we talking federal, state, both? What about when the military ships oil, or protects oil shipping lanes–is that a “subsidy”?

One thing seems clear–the total yearly figure is probably significantly higher than $ 4 billion.