.....................Right now, oil in the ground is treated as capital equipment.
This is singling out the oil industry too, and it doesn’t sound right. A fisherman can claim his boat and nets as capital equipment, but not the fish......................
The oil company has either rented the property above the oil, or paid huge lease fees to the government to attempt to find more oil under the seafloor, or on government owned property. Rather expensing these up front costs, they are allowed to claim them as capital investment, and write down over time.
The fisherman didn’t pay anything in advance to try to catch the fish, thus no capital investment.
Given that government regulations restrict how many fish of certain types can be caught to prevent stock depletion, markets have sprung up where fishing rights can be bought and sold. But I don't know the tax implications for them.