The major costs were best described by a quadratic function, which led to a U-shaped average cost curve. The cost coefficients were statistically highly significant. The author identified the intervals for which economies of scale existed and the appropriate minimum cost point. They found that diseconomies of scale appeared beyond moderate firm size. Many earlier studies of utilities found economies of scale throughout the range of observations. This study, as well as another one for the year 1970,46 found the possibility of scale diseconomies in firms of larger size.