Four maize silages from the UK and France were evaluated using the gas production method to estimate the rate and extent of dry matter degradation in vitro. There were significant differences in gas production after 17 h incubation. The silages showed similar times to produce 50, 95 and 100% of total gas production, whereas the lag time for Ema was significantly (P < 0.001) lower than that for Volgate. The potential gas production value (a + b) for Nancis was significantly (P < 0.05) lower than that for Volgate. There was a significant correlation (r = 0.996, R2 = 90.71, P < 0.001) between gas production and total VFA production. There were considerable differences in the fermentability of carbohydrates between different maize silages. Nancis and Ema had more readily fermentable carbohydrate, which yielded high propionate production and a shorter lag time. 6196 and Volgate had more slowly fermentable carbohydrate, which did become available to microorganisms but after a longer lag time.