CCUS stands for Carbon Capture, Utilization, and Storage. It’s a set of technologies that intercept carbon dioxide before it reaches the atmosphere (or pull it directly from the air), then either put that CO2 to productive use or lock it away underground permanently. As of early 2025, just over 50 million tonnes of CO2 capture and storage capacity is in operation worldwide across roughly 45 commercial facilities, spanning industrial processes, fuel production, and power generation.
How Carbon Capture Works
There are three main approaches to capturing CO2, and the right one depends on when in the process you grab it.
Post-combustion capture is the most widely discussed method. It pulls CO2 out of exhaust gases after a fuel has already been burned, using techniques like chemical absorption, membrane separation, or cryogenic distillation. This is the approach most relevant to existing power plants and factories, since it can be retrofitted onto infrastructure that’s already operating.
Pre-combustion capture works differently. The fuel is partially oxidized first to produce a mix of carbon monoxide and hydrogen (called syngas). The carbon monoxide is then converted to CO2 and separated out before the hydrogen is burned for energy. This method is common in industrial hydrogen production and certain gasification plants.
Oxy-fuel combustion takes a more elegant approach: instead of burning fuel in regular air (which is mostly nitrogen), it burns fuel in pure oxygen. The result is exhaust that’s almost entirely CO2 and water vapor. Remove the water, and you’re left with a concentrated CO2 stream that’s much easier to capture than the dilute mix you get from a conventional smokestack.
Most modern capture systems target at least 90% efficiency, meaning 90% of the CO2 that would otherwise enter the atmosphere gets intercepted. Some facilities have exceeded 95%, and engineers believe 98 to 99% capture is technically achievable. That 90% threshold has been the industry baseline for decades because it’s the point where the investment in building and installing a capture system starts to justify itself.
What Happens to Captured CO2
This is where the “U” in CCUS comes in, and it’s what distinguishes the technology from plain CCS (Carbon Capture and Storage). Rather than treating CO2 purely as waste, utilization turns it into a commercial input.
About 230 million tonnes of CO2 are already used commercially each year. The largest consumer is the fertilizer industry, which uses around 130 million tonnes annually in urea manufacturing. The oil and gas sector is second, consuming 70 to 80 million tonnes for enhanced oil recovery, a process where CO2 is injected into aging oil fields to push out additional crude.
Beyond these established uses, CO2 is finding its way into newer applications. It can replace water in concrete curing, a process where precast concrete products absorb CO2 during hardening. CO2-cured concrete is one of the most mature and promising newer uses. Captured carbon can also serve as a raw material for synthetic fuels, which are particularly interesting for aviation, where switching to electricity or hydrogen is extremely difficult. Producing these fuels requires significant energy input, but they offer a path to lower-carbon flying that few alternatives can match.
How Underground Storage Works
When CO2 isn’t being used in products, it gets injected deep underground for permanent storage. The most promising formations are deep saline aquifers: layers of porous sandstone saturated with saltwater, typically found between 500 and 3,000 meters below the surface. At those depths, pressure and temperature keep the CO2 in a supercritical state, a dense, fluid-like phase that takes up far less space than it would as a gas.
Research from Stanford University found that storage efficiency peaks at an optimal depth of around 1,600 meters. Below about 1,300 meters, costs start climbing steadily with depth. The estimated cost of geological storage itself ranges from roughly $2 to $7 per ton of CO2, depending on the depth and characteristics of the basin. That’s a relatively small addition on top of the capture costs.
One key safety consideration is making sure the CO2 stays put. While natural underground CO2 accumulations exist in many parts of the world, large-scale human-made storage still raises concerns about plume migration and potential leakage. Monitoring teams use a combination of tools to track injected CO2 over time: repeat 3D seismic surveys (which detect changes in how sound waves travel through rock), electromagnetic surveys (which pick up changes in electrical resistance as CO2 displaces saltwater in pore spaces), microseismic monitoring, and satellite-based ground deformation measurements. Together, these techniques can track the CO2 plume’s lateral and vertical movement from the reservoir all the way to the surface.
The Energy Tradeoff
Capturing CO2 takes energy, and that’s one of the technology’s biggest practical challenges. For a conventional coal-fired power plant, adding post-combustion capture and compression drops the net thermal efficiency from a range of 30 to 45% down to 25 to 35%. That translates to roughly a 30% parasitic energy loss, meaning the plant needs to burn significantly more fuel to produce the same amount of electricity while also running its capture equipment.
This energy penalty is a central reason why costs remain high and why CCUS has been slower to scale than other clean energy technologies. The extra fuel burned partially offsets the emissions being captured, though the net reduction is still substantial.
What It Costs
Capture costs vary enormously depending on the source. The Congressional Budget Office puts the range at roughly $15 to $120 per metric ton of CO2 captured, with transport and storage costs on top of that.
The cheapest applications, around $15 to $35 per ton, are in industries where CO2 is already concentrated in the exhaust stream: natural gas processing, ammonia production, and ethanol production. Separating CO2 from these streams is relatively straightforward because the gas is already present at high concentrations.
The expensive end, $50 to $120 per ton, covers power generation and heavy industries like cement, iron, steel, and hydrogen production. In these cases, CO2 is more dilute in the flue gas, making separation harder and more energy-intensive. Power plants, despite being among the largest single sources of emissions, sit toward the top of that cost range.
Where CCUS Fits in the Bigger Picture
CCUS is not a replacement for renewable energy or energy efficiency. It’s designed to address emissions that are hardest to eliminate any other way. Cement production, for instance, releases CO2 as a chemical byproduct of the process itself, not just from burning fuel. Steel mills, chemical plants, and refineries face similar challenges. For these industries, CCUS may be one of the only viable paths to deep decarbonization.
Direct air capture, a related technology, goes further by pulling CO2 directly from ambient air rather than from a concentrated industrial source. It’s far more expensive and energy-intensive, but it can theoretically be deployed anywhere and can address emissions that have already been released. The IEA groups it under the broader CCUS umbrella, alongside bioenergy with carbon capture, which pairs biomass energy production with underground CO2 storage to achieve net-negative emissions.
With just over 50 million tonnes of annual capacity operating globally, CCUS remains a small fraction of what climate models suggest is needed. But the technology works, capture rates above 90% are proven, and costs in favorable industries are already competitive with other decarbonization strategies.