Vespene Gas

This is the secondary economic resource. You need Workers to mine this in order to research tech/upgrades, or to make units. You want three Workers per Vespene Geyser.

Overview
Vespene Gas (or "Gas" for short) is one of the two main economic resources of KoL, the other being Minerals. Each race builds a structure over the geyser to mine it. A standard geyser only has 2500 units of Gas, but each base comes with two geysers. Gas is mined in units of four.

A depleted geyser can no longer continue to be mined once depleted; the building acquires a reddish tint and the workers harvesting from it cease their work until given new orders. It takes three Workers to optimally harvest a Vespene Geyser. Gas is the main limiting resource when purchasing late game tech, upgrades, and units. It's used as a balance gate for these mechanics.