|An LV-909 burning oxidizer and liquid fuel|
Oxidizer is a resource that fuels liquid fuelled rocket engines. A liquid fuel engine burns 11 parts oxidizer for every 9 parts liquid fuel. It was added with version 0.18, prohibiting rocket engines being fuelled by jet fuselages alone.
It is stored in liquid fuel tanks together with the usually correct amount of liquid fuel. Tweakables introduced in version 0.23 allow for altering during construction the amount of oxidizer or liquid fuel in a tank independently of each other. Oxidizer can also be transferred between tanks independently of transferring liquid fuel, so ratios can be throw off if not done carefully.