- CAA
- CAIR
- Calibration
- Calibration curve
- Calibration gas
- Calibration range
- Calorie
- Carrier gas
- CAS
- Catalyst
- Certificate of analysis
- Certificate of conformity
- Certified concentration
- Certified Reference Material (CRM)
- CGA
- CGA number
- Check valve
- Chemical Abstract Service (CAS)
- Chromatogram
- COA
- COC
- Coefficient of flow (C)
- Column
- Combustion
- Component
- Composition
- Compressed Gas Association, Inc. (CGA)
- Compressed gases
- Concentration
- Contaminant
- Continuous Emission Monitoring (CEM)
- Corrosive
- Critical density
- Critical impurity
- Critical point
- Critical pressure
- Critical temperature
- CRM
- Cryogenic
- Cryogenic liquid
- Cryogenic liquid container
- Cylinder