Underground

Lore & Background

The world of Factorio is a vast, resource-rich planet where the surface offers iron, copper, stone, and coal in generous deposits. But the true industrial wealth lies below. Oil seeps up from deep geological formations, accessible only through the mechanical persistence of pumpjacks driven by the player's own generators. Underground coal and iron pockets dot the terrain in smaller, denser clusters, rewarding careful surveying of the map. For the player—arrived by crash, alone, and tasked with rebuilding—these underground resources represent the first real production challenge. Surface mining is straightforward: a miner, a belt, a furnace. The oil chain, by contrast, demands planning. A single pumpjack yields a trickle of crude. That crude must be split into three distinct products, each feeding different chemical recipes. Scaling from one pumpjack to a hundred requires careful ratio management, logistics routing, and an ever-growing chemical plant array. Fans often describe the moment their first oil refinery lights up as the true 'awakening' of their factory. The hum of the pumpjack, the orange glow of the refinery, the steady drip of light oil into a chemical plant—these become the heartbeat of the operation. The Underground chain is where Factorio stops being a mining game and becomes a systems-engineering puzzle.

In Their Own Story

The dust had settled around the crash site, but the oil hadn't. You could see it glistening in the shallow pool where the pumpjack's intake pipe had punched through the cracked earth. The first unit sputtered, coughed black smoke, then settled into a steady, rhythmic thump-thump-thump that you could feel in your boots. You stood back, watching the crude oil crawl up the pipe in a slow, amber stream. One barrel. Two. The refinery's indicator light blinked amber, then green, and the first split happened—three thin streams of liquid branching into separate tanks, each a slightly different shade, like honey, like tar, like something in between. Somewhere in the distance, a chemical plant hissed to life, and the smell of sulfur rolled across the flat plain. You smiled. The surface gave you iron and copper. But down here, in the dark and the heat, the planet was offering you the future.

Reader's Guide

The Underground oil chain follows a clear three-stage pipeline. Stage 1: Pumpjacks extract crude oil from underground oil patches. Each pumpjack has a fixed output rate and requires fuel (coal or wood) to operate. Stage 2: The Oil Refinery takes 1 unit of crude oil and produces 1 Light Oil, 1 Heavy Oil, and 1 Petroleum. The refinery has a relatively long crafting time, making it the most common bottleneck in the chain. Stage 3: Chemical Plants process the three refined oils into downstream products such as sulfur, sulfuric acid, and plastic, each with its own recipe and crafting time. The optimal production ratio is 1 pumpjack : 1 oil refinery : however many chemical plants your downstream recipes demand. Because the refinery splits one input into three outputs, the chemical plant array must be sized to consume all three streams without starving. In practice, the oil refinery is the bottleneck at every scale—its crafting time is longer than a pumpjack's cycle, and chemical plants can often outpace it. As the factory grows, the chain scales linearly: double the pumpjacks, double the refineries, double the chemical plants. However, logistics complexity grows faster than throughput. Players typically dedicate entire belt corridors to routing the three oil products to their respective chemical plant groups, and the underground coal deposits that fuel the pumpjacks and refineries become a secondary supply chain of their own. At end-game scale, the Underground chain can occupy hundreds of machines and dozens of logistics routes, making it the single largest subsystem in many factories.

Did You Know?

• Underground coal and underground iron are distinct resource node types in Factorio, separate from their surface counterparts, and can appear in different map locations.
• The Oil Refinery is one of the few machines in the game that takes a single input and splits it into three different products simultaneously, making it a natural logistical branching point.
• Pumpjacks require a continuous fuel supply to operate, meaning the Underground oil chain indirectly depends on a functioning coal or wood supply chain for its own energy.
• In Factorio's progression, the oil chain gates access to plastic, sulfur, and sulfuric acid—ingredients required for advanced circuits, batteries, and ultimately rocket fuel.