The Age of Oil — Base Expansion in 46 steps

The Age of Oil unlocks on day 57 of Season 2 and needs a Level 30 Tech Center. It is nineteen research nodes ending in Base Expansion, which raises your base level cap from 30 to 35 — the biggest single progression unlock since T10.

It is also the first tree in the game whose research is paid for in a resource you have to produce: oil.

What you are looking at

Nineteen research nodes on thirteen rows, ending in Base Expansion. It is the only tree in the game paid for in oil, a resource your Oil Wells produce rather than something you already have banked, and the only one that raises your base level cap.

Two things make it unlike every other tree in this series. There is no route to choose — every node is a prerequisite for the next, so you cannot plan around skipping a branch. And almost none of it needs levelling. That second point is where the time goes, and the tree gives you no help with it: the nodes you must max and the nodes you must not look exactly the same.

The rest of this guide is the route itself — every step in order, which nodes to take all the way and which to leave at one, the oil each rung costs, and the two things that genuinely set your finish date. Both of those turn out to be the opposite of what the tree suggests, including the one most players spend their first month chasing.