With update 0.17.60, the devs changed the Basic Oil Processing recipe (unlocked with the first Oil tech) so that instead of outputting Heavy/Light oil and Petroleum gas, it only outputted Petroleum gas and subsequently rebalanced the tech tree and some recipes to reflect this (moving some techs to be later/requiring chemical science, changing recipe requirements/outputs, etc). The point of this mod is to undo all of that, bringing back the complexity challenge of dealing with a 3 fluid output, and also reverting the other tech/recipe changes the devs had done as a result.
There are a handful of settings to be able to control exactly which parts get reverted back. Note that some settings lump several things in with them (eg, all of the robotic techs, electric engine, and lubricant are affected by the same setting) in order to reduce complexity and odd combinations. Also note that there is no setting to not revert basic or advanced oil processing. For basic, the reason this setting is left out is because it'd be the same as not activating the mod (all subsequent changes stemmed from this one), and there's no option for advanced due to the heavy oil ratios (imo, it would be unbalanced to have basic give heavy oil now and not reduce the heavy oil output from advanced).
I've attempted to capture the changes in the recipes in the images above, however, the tech tree changes are a bit too numerous and varied to properly capture that way. As such, please see the change log for everything else. The first 3 revisions of this mod have basically everything.
I will not do request changes (ie, "can you make this recipe require that"), as that goes against the spirit of the mod.