A logistic model is estimated to determine factors that have influenced the formation of bilateral international water treaties over the last 60 years. Results indicate that the larger a water basin is as a percent of a country's size, the more likely the country is to form a treaty regarding its management. On the other hand, the more control over the water basin any given country has, the less likely it will be involved in a treaty. The results also support aspects of two competing theories about the role of country differences, that in some cases they serve as obstacles to treaty formation yet in other cases they encourage treaty formation to formalize management when informal arrangements are not adequate.