| www.subaqua.co.uk | reference | gas properties |
| Air | Oxygen | Nitrogen | Helium | Carbon Dioxide | Argon | Neon | Krypton | Hydrogen | Xenon | |
| Fraction of air (at sea-level) | 1 | 0.20946 | 0.78084 | 5.239x10-6 | 0.33x10-3 | 9.34x10-3 | 18.18x10-6 | 1.139x10-6 | Hydrogen | 0.086x10-6 |
| Density (grams/litre) @20oC | 1.205 | Oxygen | Nitrogen | 0.0164 | Carbon Dioxide | Argon | Neon | Krypton | Hydrogen | Xenon |