A nice system that faithfully recreates the Warcraft II oil mechanic. There are, however, some issues that need to be addressed.
You're missing importing instructions. For example, which units and abilities do I have to import? Putting all categories into a parent folder would be nice to make it easier to copy/paste.
Your system is missing a configurable part. The free parameters appear randomly scattered throughout your code. Turn these into GUI variables in a config folder and replace the hard-coded numbers with those variables. See the
GUI style guide for variable naming etc. For unit oil costs, an array of unit types and oil costs would be the best solution.
I imagine this is a system that a user wants to customize to work within the confines of their map. For example, someone might want to use your oil tankers and oil patches, but use a different method to display the player's oil. How would a user achieve that? Some more documentation throughout your code would be helpful.
You need to put the unit indexer variables in a different folder than your own variables.
Chat Message Testing and Order ID Testing are empty.
I haven't looked that thoroughly through your triggers yet. I will do that once the more glaring problems are taken care of.
Awaiting Update