The fingerings used by keyboard players are determined by a range of ergonomic (anatomic/motor), cognitive, and music-interpretive constraints. We have attempted to encapsulate the most important ergonomic constraints in a model. The model, which is presently limited to isolated melodic fragments, begins by generating all possible fingerings, limited only by maximum practical spans between finger pairs. Many of the fingerings generated in this way seldom occur in piano performance. In the next stage of the model, the difficulty of each fingering is estimated according to a system of rules. Each rule represents a specific ergonomic source of difficulty. The model was subjected to a preliminary test by comparing its output with fingerings written by pianists on the scores of a selection of short Czerny studies. Most fingerings recommended by pianists were among those fingerings predicted by the model to be least difficult; but the model also predicted numerous fingerings that were not recommended by pianists. A variety of suggestions for improving the predictive power of the model are explored.