The present paper compares thirteen shielding gases and their impact on FFR and fume particle while welding in the spray transfer regime. There was no obvious influence from the shielding gas on particle composition and fume particles were identified as (Fe,Mn)3O4. There was a slight peak shift that indicated that small levels of Mn, as detected by TEM-EDS, substituted for Fe in the Fe3O4 phase. Shielding gas composition is an important parameter for successful gas metal arc welding (GMAW) and has been shown to affect the fume formation rate (FFR). In Ar-based mixtures, increasing CO2 had a greater impact than raising O2 on FFR. When O2 was increased in ternary mixtures, the FFR increased for Ar– 5%CO2 but no discernable increase was observed for the Ar–12%CO2 mixtures. Results indicate that CO2 additions in Ar-based shielding gases are the controlling factor in determining FFR due to the effect of CO2 on welding arc characteristics. Ar–He–CO2 mixtures had the most stable FFR’s.