Changes in commercial bank market shares of farm debt are decomposed into portfolio decisions loanable funds availability and loan market size for 64 counties in Arkansas from 1986 through 1990. A seemingly unrelated regression model is hypothesized to identify county characteristics that are related to changes in commercial bank market shares. Regression results indicate that county differences in economic activity, the relative risk associated with agriculture, farm structure and regional location contributed to changes in commercial bank market shares. The results imply a market niche for rural commercial banks emphasizing agricultural loans in the presence of unlimited branch banking.