Organization of American States 
Offensive Air Support 
Office of Applied Studies 
Offensive Avionics System 
Obstacle assessment surface 
Office of Aircraft Services 
Old Age Security 
One-to-All Scatter 
Option Adjusted Spread 
Office Automation System 
Office of Administrative Services 
Open Application Server 
Orbiter Aeroflight Simulator 
Orbiter Atmospheric Simulator 
Orbiter Avionics System 
Organisation of American States 
Obstacle Assessment Surfaces 
Office of the Assistant Secretary 
Online Assessment System 
Operational Areas 
Operations Applications 
optical alignment sights 
Oracle Application Server 
Orbit Analysis System 
Orbital Analysis System 
Orbiter Attachment System 
O-acetyl-L-serine 
O-acetylserine 
oceanic automation system 
Offensive Avionics Suite