Let the oil run out

[NoQ]

In fact, it is easy to know if an oil derrick is built or not, and use timer to decrease the variable assigned to every derrick position on every tick. This is moddable (at least, on 3.1+), but of course there is no good way to set the initial amount to be different for different derricks.

[Jorzi]

This is only a vague memory from when I was a kid, but if I remember correctly, the demo had a limit on oil resources...