Vespene gas

Vespene gas (or just "gas" for short) is one of the two main resources of StarCraft, the other being minerals.

Overview
According to Doran Routhe, a famous United Powers League scientist, planetary systems beyond Sol could contain new resources that could benefit a resource-depleted Earth. Although the terran colonists went beyond their intended destination, Routhe's theories were proven correct, the Koprulu Sector featuring resources not found on Earth, including vespene gas.

Vespene gas is usually green in color, though has also been observed to be silver. It is highly prized by terrans due to its unusually high potential energy rating and as such, is used as a fuel in high-performance engines, energy reactors and simple vehicles in a manner similar to Earth's fossil fuels. Often found in geysers, deposits of vespene can be found on many planets along the galactic rim and in asteroid fields, a number of space platforms having been built to harvest the resource. In addition, vespene can be extracted directly from a planet's crust, albeit with more difficulty. Purity of the vespene is highly valued.

Vespene gas is also used by other races. The zerg have adapted themselves to use raw vespene as a source of nourishment to drive their greatly accelerated metabolisims, raw vespene exposure resulting in enhancement of the ultralisks physical capabilities. In contrast, the protoss use vespene as a catalyst for their psi-driven machines.

Vespene formations slowly regrow over time on planets such as Antiga Prime, contributing greatly to the ability of terrans to survive in the Koprulu Sector. However, while vespene geysers effectively have an unlimited amount of gas within them, after a certain point, the geyser "collapses," only trace amounts of vespene able to be found.

Vespene gas is somewhat flammable if fire of a high enough temperature is applied.

Mining / Gathering
In order to transport and store vespene gas, it must first be converted into a liquid form. Each race has a type of structure for performing this conversion: the terran refinery, the zerg extractor, and the protoss assimilator. Each geyser has a fixed amount of gas readily available (usually 5,000), and it is collected 8 units at a time and brought to the base by a worker (terran SCV, zerg drone, or protoss probe); only one collector unit can be inside the building collecting at any one time, but multiple workers can be queued up to mine from it (usually no more than 4). Once the fixed amount of gas is expended, the source is said to be depleted after which only 2 units of gas are collected at a time.

Usage
Generally speaking, the more advanced a unit is and the more abilities it has, the more vespene gas it requires to produce. Flying units and spellcasters require vespene to create. Basic structures do not require vespene gas to construct (except the hydralisk den, and the Cybernetics Core and the Radar Tower at StarCraft II), while advanced structures usually do. Terran units also require vespene gas to repair units that were built with vespene.

Beginning
Because a player with no vespene gas should be able to construct a base (and players start with 50 minerals and no gas), the workers, the base structure ("town hall"), and the vespene gas converter structure never require vespene gas to construct. Each race also has a simple ground soldier that requires only minerals to produce, the terran marine, the zerg zergling, and the protoss zealot.

StarCraft II Gameplay
Most maps will have two vespene geysers at each starting location and at each expansion. A standard gas value is 2500 vespene gas units. The optimal number of workers at each geyser is three (so six for both geysers). A depleted geyser will show "Gas: 0" instead of the word "depleted".

Vespene Geysers use the Adjutant's portrait.

Workers can pick up 5 units of gas from a geyser (only 2 when depleted). The amount of gas picked up per trip was reduced because workers now have much better pathing AI (so this reduces the pick up rate to approximately that in StarCraft I).

Vespene geysers constantly run out of gas (they each have a "remaining" and "available" figure). The latter is much smaller than the former. When the geyser runs out of available gas, the geyser must be "tapped" to extract additional gas, taking time.

All gas collecting structures (assimilator, extractor and refinery) have a "Restore Gas" ability which, at a cost of 100 minerals, will restore 300 gas but also prevents the gas collector from collecting gas for 60 seconds. This ability is available only on depleted Geysers. When the "deposit" runs out, the geyser shuts down for a few seconds, and the workers wait, after which the small allowance is provided again. The vespene collector turns red during this period. This ability is "auto-cast".

Blizzard Entertainment is still working on the gas mechanic.

High Yield Gas
The mechanism may change to allow for "higher-yield" vespene geysers.