Originally created by Roxor128:
https://mods.factorio.com/mods/Roxor128/Petrol%20Condensation

Petrol Condensation adds two new recipes to Factorio for turning lighter oil fractions to heavier ones.

80 Petroleum Gas + 1 Coal -> 60 Light Oil
120 Light Oil + 1 Coal -> 100 Heavy Oil

After Advanced Oil Processing, you can research the condensation tech to unlock its recipes. The coal requirement can be disabled in mod settings.