A metal powder additive manufacturing system and method are disclosed that use increased trace amounts of oxygen to improve physical attributes of an object. The system may include: a processing chamber; a metal powder bed within the processing chamber; a melting element configured to sequentially melt layers of metal powder on the metal powder bed to generate an object; and a control system configured to control a flow of a gas mixture within the processing chamber from a source of inert gas and a source of an oxygen containing material, the gas mixture including the inert gas and oxygen from the oxygen containing material. The method may result in an object having a surface porosity of no greater than approximately 0.1%, and an effective density of greater than approximately 99.9%.