Allow me to introduce you to the ***[Diesel Tree](https://en.wikipedia.org/wiki/Copaifera_langsdorffii)***, a tropical plant that naturally produces some petroleum-like precursors (turpenes). It's not exactly high yield, but it *is* a fuel source that ***literally grows on trees***.

[![copaiba sao paulo][1]][1]

Public Domain - By Mauroguanandi

Seeing as there's no "hard science" tag, and we're talking about people who can ***terraform whole planets***, I'd recommend a genetically modified version that has both a higher oil yield and a wider climactic range (*seeing as it can't be "the tropics" everywhere*)


  [1]: https://i.sstatic.net/XWeNNFGc.png