NOTE:
An ore-filled War Miner = 1000 credits
An ore-filled Chrono Miner = 500 credits
Play a map, preferrably in single-player skirmish mode, that has at least one oil derrick and capture only one oil derrick. Make sure that your only income is coming from this derrick. Take a note of exactly how much cash you currently have. Now, with an empty miner, begin harvesting the nearest ore/gold. If you were using a Soviet Miner, by the time your miner gets to the ore patch, fills itself up, returns to your refinery and is about to unload, you will notice that your oil derrick has accumulated less than 333 credits (aprrox. 1/3 of 1000). If you were using an Allied Miner, just before it chrono-shifts back, your oil derrick should have accumulated less than 166 credits (approx. 1/3 of 500)
As shown above, each time a miner gathers a full load of ore (either 1000 or 500), an oil derrick will only have generated less than 1/3 of this load, which actually suggests that an oil derrick is equivalent to less than 1/3 of a miner. But taking into account the following...
- distance to/from ore (when the nearest ore is finished, the miner will have to travel even further)
- distance to next ore patch once current patch is finished
- miners getting in each others way
- miners having to wait for each other to finish unloading
- and several other factors that can happen during a match
Therefore, suppose that your only source of income were standard oil derricks, to generate the same amount of credits as 1 miner, you will need approx. 3 oil derricks. In other words, 1 oil derrick = 1/3 miner.
Feel free to comment or correct me if you believe that my mathematics is incorrect.