What mean the second bar in the oil pump?

[ravenbs]

Even without any modules, there is a second progress bar in oil pumps.
I could not figure out what this mean, not by looking at the wiki, forum or youtube.

So - what does this thecond lila progress bar mean?

[DaveMcW]

Research "mining productivity" and it will start filling up with free bonus resources.

[ravenbs]

Thanks a lot, makes sense