"Environmental costs"? You mean the damage allegedly done by the release of CO2 during combustion? Quantifying that assumes damage is actually done by CO2.
Subsidy: money given by government to produce or reduce the purchase price of something that otherwise would not be produced. or...given to reduce the production of a commodity to prevent price collapse (control of supply).
I don't see standard deductions taken by other industries, such as operating expenses, an alleged price break on lease sales, even lowball royalty agreements as subsidies, because those are either ordinary deductions or just piss poor negotiating to establish royalty and/or lease agreements. Leases are usually sold on a bid basis, anyway. Either way, if a commodity is being subsidized, the price point would be below the supply cost.
Pollution costs only matter if the government is paying to clean those up, without some sort of subrogation. There are fines, etc. and occasionally direct payments from lawsuits, but generally, that is not a result of best industry practices, and rather, the result of accidents. For instance, the easiest numbers to beat out of Google's AI, showed 11 blowouts in ND since 2006, of 11,000 wells drilled. While 0.1% seems good, It can be improved, and I don't have any numbers on the amount, or whether these were drilling rigs or well servicing activities, nor even what fluids (nor how much) were released. Those have costs associated with them, but the State will be asking for money over that, not handing it out. It falls under accidents, and the cleanup costs fall on the oil company.
"Global Warming" costs are patent nonsense. Much may be blamed on that, but none of it is proven, and not for lack of trying.
In the US, the price point is just above supply costs, not below. If fuels here were subsidized, the price point would be below supply costs, because the Government (taxpayers) would make up the difference.