We estimate nonparametric measures of returns to scale for U.S. commercial banks using a new approach. We find significant scale economies across the entire bank size distribution. Scale economies are persistent over time, have an L-shaped relation with bank size, and contribute significantly to TFP growth. Our results indicate that even the largest banks may growth even further and that the industry is unlikely to retrench. Our empirical approach has four distinctive features; viz, we 1) control for unobserved heterogeneity across banks, 2) use a fully nonparametric specification of the underlying bank's technology, 3) estimate TFP components nonparametrically, and 4) focus on the post deregulation era of the U.S. banking industry (2001-2010).