This paper provides estimates of bank efficiency and productivity in the United States, over the period from 1998 to 2005, using (for the first time) the globally flexible Fourier cost functional form, as originally proposed by Gallant (1982), and estimated subject to global theoretical regularity conditions, using procedures suggested by Gallant and Golub (1984). We find that failure to incorporate monotonicity and curvature into the estimation results in mismeasured magnitudes of cost efficiency and misleading rankings of individual banks in terms of cost efficiency. We also find that the largest two subgroups (with assets greater than 1 billion in 1998 dollars) are less efficient than the other subgroups and that the largest four bank subgroups (with assets greater than $ 400 million) experienced significant productivity gains and the smallest eight subgroups experienced insignificant productivity gains or even productivity losses.