| AFC | annualized fixed cost (depreciation) |
| AOC | annual operating cost |
| Btu | British thermal unit |
| CO2 | carbon dioxide |
| | purchased cost of equipment q |
| FCI | fixed capital investment |
| FCIi | fixed capital investment for a given processing unit |
| FCIS | salvage value of the fixed capital investment |
| ΔFLmix | average explosiveness of a mixture |
| | Hand factor for equipment q |
| gal | gallons |
| GJ | gigajoules |
| h | hours |
| H2S | hydrogen sulfide |
| HA | high acid |
| HVm | average mass heating value |
| IROI | incremental return on investment |
| kWh | kilowatt hours |
| lb | pounds |
| LFLmix | lower flammability level of a mixture |
| | mass flow rate |
| MDEA | methyl diethanolamine |
| MM$ | million dollars |
| MMBtu | million British thermal units |
| MMSCFD | million standard cubic feet per day |
| MSCF | thousand standard cubic feet |
| N | plant lifetime (number of years) |
| N2 | nitrogen |
| NGL | natural gas liquid |
| N np | number of non‐particulate processing steps |
| N OL | number of operators per shift |
| P | number of processing steps where particulate solids are handled |
| P | average pressure |
| PRI | process route index |
| psig | pounds per square inch of gauge pressure |
| ROI | return on investment |
| SCF | standard cubic feet |
| TAC | total annualized cost |
| TEG | triethylene glycol |
| TCI | total capital investment |
| ΔTCI | change in total capital investment for a given additional case |
| UFLmix | upper flammability limit of a mixture |
| VCi | total variable cost for each process unit |
| WCI | working capital investment |
| yr | years |
| ρ | average fluid density |
