This analysis explores the valuation of feedstock quality attributes of switchgrass and miscanthus –two energy crops poised for future expansion– and compares the relative economic availability of these two crops under two scenarios: 1) uniform price assumptions (i.e., no incentive for quality), and 2) a scenario of a price premium based on convertibility (i.e., an incentive for quality). Given data on cellulose content, hemicellulose content, and their relative convertibility, miscanthus is expected to be 11% more efficient at conversion to biofuels than switchgrass under biochemical conversion route. Based on this scenario of improved conversion efficiency and associated profit, we simulate an 11% price premium for miscanthus over other feedstocks in a base-case scenario. By adding this price premium, supplies of miscanthus increase over the base case by about 4 million (44%), 94 million (64%), and 166 million (94%) tons in year 1, 11, and 21 after simulated contracts for production are initiated respectively. These results emphasize that custom simulations are needed to quantify feedstock availability if supplies are intended to reflect grower response to industry demands for feedstock quality specifications. Farmers can grow “peas or carrots”, and price signals from biorefineries will influence what energy crops they produce. Recognizing that energy crop mix is tractable according to quality characteristics is relevant both for near-term and long-term biofuels research and development. We recommend accounting for market preferences for quality attributes when estimating potential future supplies of energy crops.