The effects on durability of composition variations in West Valley Nuclear Services Company preliminary waste glass composition WV205 are discussed. MCC-3 results at times from 7 to 180 days are presented for 50 glass compositions. The results are suggestive of a large plateau region where durability is good and weakly dependent on composition, adjoining a region in which durability is a much steeper function of composition. The same effect is observed when the redox state of the iron, which comprises ∼12 wt% of the glass, is varied. The general trends are discussed in terms of the structural roles of the components. The effects of the alkalies and alkaline earths correlate quite well with the field strengths of these ions.