The environment in which organic light emitting diodes (OLEDs) are fabricated can profoundly affect device performance, as shown here. The previously reported asymmetric injection behavior of Mg:Ag/Alq(3)/Mg:Ag structures (where Alq(3) is tris(8-hydroxyquinoline) aluminum) is investigated by fabricating and testing these structures under ultra-high vacuum with and without exposing the bottom electrode to, oxygen and water vapor. It is demonstrated that devices fabricated under strict Vacuum conditions exhibit symmetric I-V characteristics while those exposed to air do not.