If this is the ideal size, then the ideal number of electric utilities in the U.S. is about 30. Yet, there are well over 80 investor-owned utilities in the U.S. today, plus a large number of gas distribution companies, and a few interstate gas pipelines and water companies. In addition, many electric utilities own or are anxious to buy gas companies in order to be full energy service providers. Buying a gas company that overlaps the electric utility's service territory is particularly attractive to the electric company since even more costs can be cut. They can invest in the likely consolidators - those companies committed to cutting costs and growing earnings and dividends through acquisition.
Size is a big factor.
If the optimum size is 5 to 6 million customers, utilities with sound balance sheets that have two to three million customers can realistically acquire another two or three million over time to attain optimal mass. Utility mergers take a long time to close and then a long time to digest, and there isn't enough time to consolidate your way into the top tier unless you are already halfway there. A small or mid-sized utility may acquire a smaller utility or do a merger of equals along the way. Ultimately, however, most of the small and medium size utilities are destined to be acquired by bigger companies. One might assume that small utilities serving faster growth markets would be the most likely targets.