So, I tried to reconstruct this situation in the editor, and it seems to do weird things when multiple pumps take oil from one pond, especially when the pond is rather empty/only floor covered with oil. Then pumps start to not putting out the oil at the output pipe. The energy system in this case seemed to work fine, the pumps unfortunately didn't. In this case, I didn't use compensators but rather used 7 steamengines connected to pumps pumping oil from the oil source to the engines directly. The pumps generated energy in this case because they were below the input pipe from the pumps. Saving somehow created a script which caused a (maybe too much recursions) error which made it impossible to reload the scenario. I'll try to create a scenario next time that creates all the things needed via "hand-written" script.