This dissertation seeks to identify fluctuations and volatility in the prices of commodities in early Ptolemaic Egypt (332-186 BCE) and to explain the possible causes of such variability. An understanding of the interplay between market forces and institutional influence on the prices is fundamental to understanding the ancient Egyptian economy and ancient economies in general. In tabulating and analyzing ancient prices, I use the approach of the New Institutional Economics to address the key economic question of how prices were formed, including the role of the state and other social institutions in regulating the extent to which prices could vary. The factors that could have influenced price variability are endless--inundation levels would have had the largest impact on harvest levels, and certain crops may have been more or less affected by these environmental factors based on their own biology, for example. This dissertation approaches price variability from an alternative angle, however, interrogating the extent to which the Ptolemaic state was effective in overriding the variability caused by such infinite factors through its interventions towards price stability (e.g., fixing prices or managing production of certain commodities). ,In order to approach such macroeconomic questions, I needed to collect a broad set of data. I was able to leverage the Trismegistos online metadata database project, which contains information from a number of databases of ancient texts, including the Database of Demotic and Abnormal Hieratic Texts and the Heidelberger Gesamtverzeichnis, thus tabulating essentially all known Greek and Demotic texts from the period. My searches yielded a total of 10,430 texts; of that total, I was able to check 8,557 texts for price data. My dissertation is based on over a thousand commodity prices I found in those texts. ,Some of the best-known studies of Ptolemaic prices have focused on rates of conversion between grains and money known in penalty clauses in contracts—these rates increase in a rhythmic, stepped manner. However, my price data demonstrate that market prices did not move according to the same patterns as the penalty prices. I argue that since penalty prices cannot be extrapolated to represent actual market prices, these were different systems of pricing—and that ultimately, there was no sense of “normal price” in Ptolemaic Egypt.,In the end, I note that Ptolemaic prices were both subject to inflation and highly variable, and I evaluate the possible reasons for this inflation and generally high variability. Coupling the quantitative price data with qualitative evidence from many texts, I argue that the state’s ostensible interventions were not effective in generating adequate elasticity of supply. I further emphasize the incompleteness of information available to ancient individuals as they set and accepted prices, as well as possible imbalances in access to that information. This dissertation argues for the importance of acknowledging the vast differences in the amount of information available to people acting in ancient and modern economies and discusses the potential effects of engaging in transactions with high uncertainty, such as speculative effects. Thus, while this study encompasses only one society, it sheds light on issues fundamental to the study of economies generally by using a blend of quantitative and qualitative methods to understand both concrete and theoretical questions about how economies work.