An easy one for you veterans!
Is Fuel Production not in fact Fuel Productivity? This would change my priorities ...
Not sure what you mean.
The Fuel Production technology determines the base number of liters per year your race produces with a single Fuel Refinery installation or Sorium Harvester ship module.
Actual production of a given Fuel Refinery is modified by the Production bonus of Planet and Sector governors, as well as the Manufacturing Efficiency Modifier of the population.
Actual production of a given Sorium Harvester ship module is modified by the Mining bonus of the Ship commander and of the appertaining Naval Admin commanders.
Regardless of tech or bonuses, production requires one ton of sorium for every 2000 liters produced.
Thanks, you answered my question! It could have been that a refinery always uses 20 tons per year. Without technology, this leads to 40000 liters a year, but with the next tech, it would be 48000 (so a bonus productivity/efficiency).
Ah, I see now - production would be throughput while productivity would be efficiency. To rearrange the punchline above, the efficiency is fixed and is always 2kL per ton, while the throughput per module or installation improves with technology. Thankfully, once an appropriate sorium giant is found, the efficiency is largely irrelevant.