Although these bank balances were not very profitable to the reserve banks, the correspondents were useful in giving access to business lines and houses in every part of the United States. Accordingly the central banks waged a serious campaign to attract them, particularly after the 1900 amendment to the National Banking Act and the rapid expansion of national banks that resulted therefrom. The chief inducement offered to the banks to make such deposits was the interest allowed. The bidding was at first competitive, and varying rates were paid. By a process not quite understood the rate most commonly adopted came to be 2 per cent, which rate was not determined by careful cost and profit analysis but rather by guesswork. At first interest was allowed only on balances of banks, but later on, owing to competition, interest was paid on balances of insurance companies, railroads, big capitalists, and on all accounts of unusual size. Some banks came to make general rules to pay interest on all balances above certain minimum amounts, others kept to the practice of private arrangements with each depositor.