| α | heat-to-power ratio | kWh/kWe |
| α i,j | membrane selectivity of components i and j for gas mixture | — |
| | heat of reaction | kJ |
| η cap,e | CO2 capture efficiency | —, % |
| η | efficiency | —, % |
| η cap | CO2 capture ratio | —, % |
| η is | isentropic efficiency | —, % |
| η p | polytropic efficiency | —, % |
| κ | ratio of specific heats, cp/cv | — |
| λ | excess air ratio | — |
| ξ | friction factor | — |
| ρ | density | kg/m3 |
| σ | ionic conductivity | S/m |
| σ inj | CO2 formation by combustion per tonne of CO2 injected | t CO2 by combustion/t CO2 injected |
| σ store | CO2 formation by combustion per tonne of CO2 stored | t CO2 by combustion/t CO2 stored |
| ϕ | equivalence ratio (1/λ) | — |
| φ | ratio of additional oil or gas to CO2 injected | t fuel/t CO2 |
| χ | CO2 generated per lower heating value of fuel | kg CO2/MJ |
| ψ | CO2 formation by combustion per tonne of CO2 | t CO2/t fuel |
| ω | ratio of recycled CO2 to stored CO2 | t CO2 recycled/t CO2 stored |
