This isn't what people normally mean when they refer to subsidies, but the fact that fossil fuel users are allowed to contaminate everyone's air is effectively a massive subsidy for their operations. If the cost of the CO2 and pollution were paid by those producing it, this stuff would be way more expensive.
The IMF recently published a working paper[1] on energy subsidies at global and regional levels that might be of interest. They do use an fairly broad definition of what counts as a subsidy (including cost of damages environmental damages and global warming effect of CO2 emissions).