Factorio Forums

I'm trying to understand the (combined) yield numbers for oil fields, but I can't wrap my head around it. All the quotes below reference the crude oil wiki page. Questions are bold.

First, it says:

Each oil field has a yield displayed as x%. ... The amount of oil a pumpjack extracts per cycle is yield multiplied by 10 ...

So that means if a pumpjack info pane says "expected resources: 4.0/s", then the oil field underneath it has a yield of 40%, correct?

Later, it says:

While cycles left is greater than 6000 (20% yield) and greater than 20% of the initially available cycles, each pumpjack cycle reduces the number of cycles left by one.

So that means that over time every pumpjack's expected resources will decrease to 2.0/s and at that point it's as low as it will ever be, correct?

But, assuming I understand that correctly, that means that over time the combined yield displayed on the map for an oil patch should eventually decrease to 20% * the number of oil fields there. However, none of my oil patches ever drop that low.

For example, there is one patch that I started pulling oil from very early in the game, and the pumpjacks there have been running near continuously (early on I was just throwing it in tanks and barrels for later -- all since used up) for something along the lines of 20 days of play time now. This patch has 9 fields, which, by my understanding, means the yield should decrease over time to 180%.

Except it stopped decreasing at 342% a long time ago, and despite continuously pumping oil, hasn't dropped below that:


None of the "expected resource" values on the pumpjacks have decreased below their current values in that time, either:


From the wiki my expectation is that this oil patch should be at 180% by now, or at least much lower than it is and continuing to decrease. All of my other fields show similar behavior, stopping at some value larger than 20% * the number of fields.

So my main question is: What am I missing here and why is this patch (for example) holding at 342% instead of dropping to 9*20%=180%?

JasonC wrote: ↑Fri Mar 06, 2020 7:24 pm

While cycles left is greater than 6000 (20% yield) and greater than 20% of the initially available cycles, each pumpjack cycle reduces the number of cycles left by one.

What am I missing here and why is this patch (for example) holding at 342% instead of dropping to 9*20%=180%?

I bolded what you are missing. Maybe a reworded explanation helps?

https://wiki.factorio.com/Pumpjack wrote:Extracting oil lowers the field's yield by 1% per 300 pumpjack cycles to a minimum of 20% of the initial yield or 2 oil per second, whichever is larger.

There's a lot of ambiguity in the oil's original design. Right now the % value you see on maps is really a field richness factor, and is not related to the 20% lower limit. That 20% limit is actually 20% -- the richness of your field will never drop below 1/5 of what it was at the beginning of the game. So... why is your oil field labelled as 342%? It is because it (probably) started at 1710%.

Well that's interesting, never realized that. I thought all oil went to 20% eventually...

Bilka wrote: ↑Fri Mar 06, 2020 8:05 pm

JasonC wrote: ↑Fri Mar 06, 2020 7:24 pm

While cycles left is greater than 6000 (20% yield) and greater than 20% of the initially available cycles, each pumpjack cycle reduces the number of cycles left by one.

What am I missing here and why is this patch (for example) holding at 342% instead of dropping to 9*20%=180%?

I bolded what you are missing. Maybe a reworded explanation helps?

https://wiki.factorio.com/Pumpjack wrote:Extracting oil lowers the field's yield by 1% per 300 pumpjack cycles to a minimum of 20% of the initial yield or 2 oil per second, whichever is larger.

Ah ha! Super clear now, thanks.

jdtitans wrote: ↑Fri Mar 06, 2020 8:15 pm There's a lot of ambiguity in the oil's original design. Right now the % value you see on maps is really a field richness factor, and is not related to the 20% lower limit. That 20% limit is actually 20% -- the richness of your field will never drop below 1/5 of what it was at the beginning of the game. So... why is your oil field labelled as 342%? It is because it (probably) started at 1710%.

And thank you, too.

This makes sense now.

So two follow up questions, then:

1. This means, then, I can't actually tell how depleted an arbitrary oil patch is just by looking at it with no context, I've got to make note of the initial combined yield first (or observe it for a long period of time to see if it looks like it stopped dropping), correct?

2. Just as a sanity check: The "read resources" mode of pumpjacks appears to always round expected resources down (i.e. ⌊resources⌋), and there's no "read entire patch" mode, which implies the circuit network can be used to monitor depletion (given the initial combined yield) by summing all pumpjack values, and even though it may detect depletion early, it will never fail to detect it. In other words, the sum of the values from all the pumpjacks will always be some value ≤ the actual value. Can somebody confirm this will always be the case?

Thanks!!