This paper discusses the important role of gas adsorption in nanotribology and demonstrates in-situ vapor phase lubrication of microelectromechanical systems (MEMS) devices. We have elucidated the molecular ordering and thickness of the adsorbed water layer on the clean silicon oxide surface and found the molecular-level origin for the high adhesion between nano-asperity silicon oxide contacts in humid ambient. The same gas adsorption process can be utilized for continuous supply of lubricant molecules to form a few Å thick lubricant films on solid surfaces. Using alcohol vapor adsorption, we demonstrated that the adhesion, friction, and wear of the silicon oxide surface can significantly be reduced. This process made it possible to operate sliding MEMS without failure for an extended period of time.