The following is a series of tips regarding fuel networks and fuel efficiency, since the number of people having issues with this has increased in recent updates. The information provided was gathered by myself and other members of the community.
Another note, this guide will not contain screenshots because the overlay currently is bugged.
Reactor Types matter
You can look at reactor stats on the tech screen. Many players probably go for Quantum reactors over fusion because of their high output, but notice the Caslon:Fuel ration. For Quantum its 5:1. This is horrifically inefficient, and practically guarantees your ships will run out of fuel when traversing any significant distance. Fusion on the other hand is the opposite, lower output but a much better conversion ratio being at 1.444/1.000.
As a general rule use fusion for ships, quantum for stations. Its also might be doable to use quantum for strike craft, just be sure to check fuel range in the statistics. Fuel efficiency generally doesn’t matter as much for strike craft.
You can put a large mining engine on mining stations, pretty much everyone already knows this. But it probably doesn’t occur to people that you can put a smaller mining engine on said station in addition to this.
Or that you can add multiple small mining engines and they do stack. There is the reason why “large mining station” hulls have so much space but not enough non-support modules.
Fuel Tanker design
First, the obvious that if you want fuel tankers dedicated to supplying only one specific fleet, it needs to be in that fleet.
Aside from that, design matters. For fuel tankers its cargo holds that matter. They transfer fuel via Caslon stored in their cargo holds, NOT fuel in their own tanks. Give them one or two fuel tanks, and as many cargo holds as you can squeeze in there alongside other necessity modules. Fuel tankers will naturally convert caslon from their own cargo holds should they run out of fuel, so don’t worry about that.
Predicting bad AI
If you sign a trade agreement with an empire that is far away from you, your freighters will try and trade with it regardless of whether or not they can actually reach it with their current fuel supply. Try to give them as many fuel tanks as possible to help with this if you must use trade agreements.
Early game especially it might be disadvantageous entirely to sign trade agreements with far away empires for this reason. Factor this in, as it can severely hamper your early game logistics network.
If you are trying to supply a location that, for whatever reason, your freighters are NOT adequately supplying (Ghost fleet base), you can always make a troop transport design with a cargo hold and small mining engine. You can manually mine whatever you need from wherever, just be sure to pay attention to the ship, because it will try and offload at a location automatically once its cargo hold is full (you can redirect it somewhere else). You can however manually specify the offload location wherever you wish.
Spaceports increase the demand for caslon at a colony by 4-8 times as much (and something like 50% more for other resources). Having a spaceport at every colony will make it much harder for your logistics. This can cause fleets to continuously pick up caslon at locations that can’t fully supply them, which can spiral out of control and starve the empire of fuel. Stagger the construction of spaceports, just like colonizing planets, to give your empire time to redistribute resources.
*Assigning a fleet to a location as a home base further increases its caslon demand.
Small mining engines
Anything can have and use small mining engines (except passenger ships and freighters), notably including monitoring stations. You can build a monitoring station once at any object, even alongside a mining station.
They will generally be ignored by the logistic system, including fleets in need of fuel, but you can manually send a fleet to refuel at these stations. They make great refuel depots in this manner. When at war, you can build these in hostile territory and they will not be a priority target. Alternatively, you can manually create a monitoring station just with cargo capacity and manually set a demand for caslon, which freighters will heed and deliver to it.
You can and should operate stations completely on energy collectors. Don’t just cover static energy on stations- they will power the station even during combat.
Carriers can effectively function as fuel tankers, especially as the core ship of a tight formation fleet, and cruisers can serve as very fast combat fuel tankers, albeit manually. Both can carry far more fuel than a tanker, and work in conjunction with the aforementioned fuel monitoring station very well.
Fleet Fuel Caps
If using massive fleets of small ships, be mindful of their total fuel capacity and use. If its total fuel capacity rivals what is in stock at your richest locations, it is an unwieldy fleet. Split the fleet(s) up.
10.5. If you’re hurting for caslon, reassign some attack fleets to defense, set any fleets not in use to manual and park them, and assign all your out-of-fleet military ships to a parked fleet. Automatic fleets and ships generally keep moving, needlessly eating up fuel.
10.6. When you design ships, you can specify the ship positions “Core”, “Close Escort” and “Picket”, where “Core” is the default. Try to avoid picking “Close escort” (maybe “Picket” too), because even when a fleet is parked, the “Close escort” ships may fly sometimes around even when “idle”.
If your empire is in dire need of caslon, design an ergonomic fuel tanker with extra mining engines, no defenses and one engine, and build 10 or more of them and set them to manual control before they’re built (or temporarily set new state ships built to Manual in the policies tab). Assign them to mine at the richest caslon source, and once they’re filled up, retire them at your capital- fuel ships will not drop off fuel. This is more cost-efficient than buying foreign caslon. It is a stopgap measure- permanent state mining ships should be kept to a minimum. Note that fuel ships will only mine caslon, while other ships will mine all resources.