What kind of fuel does KSP use for LiquidFuel?

[cantab]

Now, to determine how much of each fuel tank's mass is RP-1 and LOx and how much is tank, plumbing, and insulation...

We know the dry mass and fully fuelled mass from the game at least. And we can break it down into fuel and oxidizer masses with the tweakables. The only thing we can't get is any more detail on the dry mass.

[MarvinKitFox]

... According to the Wiki, it's 5000Kg/m³, which makes me think it's liquified selenium or something.

5000Kg/m3 is absurdly dense by Earth standards, its just a drop less dense than the average density of the planet. (5000 vs. 5500, or 91%)

By the same criteria, Kerbin's fuel should be 91% of 58500 kg/m3, thus 54000 Kg/m3

At a "mere" 5000Kg/m3, Kerbin's fuel can almost be used to fill party balloons, it is so low in density!

[TonyInTsv]

Haha, I kind of like the idea of liquefied Kerbals... "Biofuels", which is actually kind of why I'm interested.

Turns out it's incredibly hard (not impossible) to synthesize oxidizer using bacteria because oxidizing agents typically have the unfortunate side effect of death.

Not all.

Oxygen can cause death in high concentrations.

NO can cause death in high concentrations too, by displacing O2, but is quite safe to use and is used as propellant in whipped cream.

[Curveball Anders]

Probably munshine

Tekuila more likely

[Ayo99]

Liquid Hydrogen (H2) and Liquid Oxygen

Watch Scott Manley video :

[lajoswinkler]

Both fuel tank types in the game use the same fuel, and one of them says KEROSENE, so it should be RP-1 or something like that.

Oxidizer? LOX is too light and boils off. I'd say probably nitrogen tetroxide.

Not all.

Oxygen can cause death in high concentrations.

NO can cause death in high concentrations too, by displacing O2, but is quite safe to use and is used as propellant in whipped cream.

That would be N₂O. NO immediately oxidizes into NO₂ when exposed to air, and both are very poisonous.