The top 3 'subsidies' for oil are:
1) The national oil reserve
2) farmers fuel exemption
3) Home heating oil credit
Those together make up over 60% of all the 'subsidies' big oil receives.
You can debate the need for the oil reserves but that is often considered a national security issue.
The farm credit excludes farmers for paying road and highway taxes on equipment not driven on roads.
The heating oil credit is used to pay for oil for low income families.
Unlike green subsidies which are mostly focused on the producers, the bulk of oil subsidies are for the consumers. Farmers will still need to buy fuel for their equipment and families in the northern states will still need heating oil. All ending those subsidies will do is cause both of those groups to have to pay more while having little impact on big oils bottom line since the additional cost will all go to the government anyway (which will then have to be given out as some other form of subsidy/welfare payment to keep costs of food down and help people not freeze to death).