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 the color may change through contamination;  silver vespene deposits have been observed. 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. Deposits can be found via geo-survey units, courtesy of the gas's electromagnetic returns. Crystallized vespene can also be found alongside mineral fragments inside asteroids.
Purity of the vespene is highly valued. Hydrogen sulfide is one such impurity, causing the gas mixture to become explosive. Contaminated vespene has a yellowish tinge. Liquid vespene is also usable.
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 metabolisms, 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", with only trace amounts of vespene able to be found.
In order to transport and store vespene gas, it must first be sealed in a container, either a tank, box or sac depending on the race. Each race has a type of structure for performing this conversion: the terran refinery, the zerg extractor, and the protoss assimilator. Only one worker unit can be inside the building collecting at any one time, but multiple workers can be queued up to mine from it. Depending on the exact distance from the nearest base, the optimal number of units to be sent to mine a geyser is three or four. Once the fixed amount of gas is expended, the source is said to be depleted, and the workers get a quarter of the normal amount. Generally speaking, the more advanced a unit or structure is, the more vespene gas it requires to produce. Flying units and spellcasters require large amounts of vespene to create.
Typically, a standard mineral patch comes with a lone vespene geyser with 5000 units of gas. Units collect the gas at a rate of 8 units per trip until the geyser is depleted. When a geyser is depleted, the workers will continue to mine but will only produce 2 units of gas per trip.
Compared to the first game, the harvesting of vespene gas is radically different. A standard geyser only has 2500 units of gas, but each mineral patch comes with two geysers. Gas is mined in units of four rather than eight, and the cost of gas-extracting buildings is decreased. Thus, while overall collection of gas is equal to the original game, two workers collectively mining 8 units a second, gas is a more costly investment due to the need for twice as many workers and two gas-extracting buildings instead of one. 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.
In 2008, a worker would collect 6 vespene gas per trip and the geyser had an initial supply of 1000 units of vespene gas, once depleted the amount harvested per trip was reduced down to 2. Vespene collectors had an ability to "Restore Gas" in which the player would pay 100 minerals and the collector would temporarily shut down for 45 seconds. But once the shut down period was finished, 400 vespene gas would become available to be harvested at 6 vespene gas per trip until this supply was depleted again.