ΔE 8.1, close: similar, with a visible difference side by side. Mars Black is a little darker, more muted than Oil Stains.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Mars Black is a little darker, more muted than Oil Stains.
The same difference applies the other way round: Oil Stains is a little lighter, more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Oil Stains on the colour wheel See Mars Black on the colour wheel
All matches: Oil Stains equivalents · Mars Black equivalents