What it is for
Flying around inside a system is free. The moment you go through a jump gate to another system, it costs jump fuel. Every gate has its own fixed price, from 4 units on the cheapest hop up to 51 on the most expensive, averaging about 22. Nothing else in the game consumes it.
Your tank
Most hulls carry a 900 unit tank. The Marauder, Shuttle and Hawk carry 1,000, and the Prospector only 700, which is worth knowing if you fly one.
Your ship refuels itself, but only so far
Here is the part a lot of captains never notice. Your ship generates 5 units of fuel an hour on its own, for free, while you are away. But it stops at 20% of your tank.
So a 900 unit tank quietly refills to 180 and then sits there. It is a safety net, not a supply. It means you will almost never be truly stranded, and it also means you will never wake up with a full tank. If you want to go a long way, you have to put the fuel in yourself.
Making your own
There are 18 Heavy Jump Fuel Refineries in the galaxy. Each gives you four processing slots, and the recipe is fixed:
• 40 Kelsalt
• 20 Kallycite Ore
• 20 Tessarine Gas
• 10 minutes
• produces 25 jump fuel
Kelsalt is a common ore you have been tripping over since Feris. Kallycite Ore and Tessarine Gas both come out of refining, so this is a genuine reason to get familiar with a Refining Centre if you have not already.
Every batch also pays you 20 Manufacturing experience, which is not nothing if you are building towards crafting.
Run all four slots and that is 100 fuel every ten minutes from materials you very likely already have sitting in Commercial Storage.
Two places fuel lives, and this trips people up
Fuel you synthesise does not go into your ship. It goes into your Captain’s Refinery Account, which is a separate global balance that follows you everywhere and has no ceiling. Some captains are sitting on tens of thousands in there.
Your ship tank is the other place, and that is the one that actually gets burned when you jump.
To fly on your own fuel you transfer from the Account into the Tank, and the transfer is capped by how much room the tank has left.
The transfer only goes one way
Account into tank. There is no route back. Fuel that goes into your ship is committed, so do not dump 900 units into the tank the night before you decide to sell up, because it is staying there.
The practical version
Keep your Account healthy and your tank topped for the trip you are actually making. The 20% trickle covers emergencies. Four slots of synthesis while you do something else covers everything up to a serious expedition. And if you cannot be bothered making it, the Galactic Emporium has a Jump Fuel tab where captains sell theirs, though you will pay for the convenience.
One number to remember: a full 900 tank is roughly forty average jumps. That sounds like plenty right up until you accept four haulage contracts pointing in four directions.
Making it faster, if you want to
The FSP Store sells a Jump Fuel Synthesis Boost. It permanently adds +5 fuel to every synthesis run, and you can buy it up to five times, so a fully upgraded captain gets +25 per batch.