China 
Africa 
- Oxy-combustion
- Oxy-fuel combustion process
- Oxyacetylene
- Oxyanion hole
- Oxyanions
- Oxybenzone
- Oxychloride
- Oxychlorination
- Oxygen
- Oxygen balance
- Oxygen compounds
- Oxygen concentrator
- Oxygen difluoride
- Oxygen effect
- Oxygen evolution
- Oxygen isotopes
- Oxygen pulse
- Oxygen reduction reaction
- Oxygen saturation
- Oxygen scavengers
- Oxygen sensor
- Oxygen tanks
- Oxygen tension
- Oxygen therapy
- Oxygen toxicity
- Oxygen-16
- Oxygen-18
- Oxygen-evolving complex
- Oxygen-free copper
- Oxygenases
- Oxygenates
- Oxygenation
- Oxyhydrogen
- Oxylipins
- Oxymatrine
- Oxynitride
- Oxysterols
- Oxytocin
- Oyster
- Oz
- Ozone
- Ozone cracking
- Ozone layer
- Ozone monitor
- Ozone-depleting
- Ozonides
- Ozonolysis
- P systems
- P vs NP
- P waves
- P-adic analysis
- P-anisidine
- P-chart
- P-code
- P-complete
- P-coumaric acid
- P-cresol
- P-cycle protection
- P-cymene
- P-glycoprotein
- P-group
- P-hacking
- P-loop
- P-matrix
- P-n diode
- P-n junction
- P-selectin
- P-site
- P-space
- P-toluenesulfonic acid
- P-type
- P-wave modulus
- P-waves
- P-xylene
- P120
- P120 catenin
- P16
- P2
- P21
- P27
- P300
- P38 mitogen-activated protein kinases
- P3P
- P4
- P53
- P53 upregulated modulator of apoptosis
- P700
- PABA
- PACS
- PACU
- PAD emotional state model
- PAEK
- PAF
- PAL
- PALB2
- PAM
- PAM-CRASH
- PAN
- PAPR
- PAR