Heart of the Swarm Campaign- Kerrigan Abilities: Vespene Efficiency (Level 35)

Vespene Efficiency doesn’t really seem like much of an ability at first- a 25% increase in the amount of vespene you harvest isn’t a huge deal like double drones, and it doesn’t give you any odd options for increasing combat efficiency like Malignant Creep.  It is, however, useful, and can become vital to Zerg strategies.  Virtually every combat unit that a Zerg force can field requires vespene gas, and with zerglings as the only exception it’s a flat out truth that Zerg forces need vespene and they need a lot of it.

Twin Drones goes a long way to increasing the rate at which your Zerg bases produce a viable assault force and quantity of resources.  However, unless you rely very heavily on zerglings, you’re going to find that you often have so much more mineral resource than vespene gas that you can’t actually produce the units you want to- particularly in the case of hydralisks, mutalisks, and any unit evolved from another unit (including banelings).  In these situations, you’re going to wind up sitting and waiting for more vespene gas to come in despite the fact that you already have far more minerals than you could possibly need to replenish your forces.  Because of this, while Twin Drones is the best way to get your forces up to speed, you are going to want Vespene Efficiency very badly to accomplish the best use of your control value.  The amount of vespene gas added is very small when looked at in a ‘per drone trip’ sense, but it can easily turn three roaches into four, or three hydralisks into two hydralisks and four roaches.  The relatively limited rate at which vespene can be harvested (three drones per geyser, a maximum of four geysers per base compared to minerals with three drones per mineral patch and as many as twelve or thirteen mineral patches per base) and the high vespene requirements of valuable zerg units (anywhere from 2/3 as much vespene as minerals to equal quantities of both) puts a lot of pressure on your vespene production that Twin Drones simply fails to reduce.

By comparison, Vespene Efficiency does basically nothing about your rate of base buildup nor your combat value per unit- but a player who can ramp up their resource gathering just fine without Twin Drones (despite their larger control expenditure for resource harvesting) will find that Vespene Efficiency improves their state later in each mission to a degree that Twin Drones simply doesn’t manage without spending a considerable period of time waiting for more gas to come in from the extractors.