The potential of replacing petroleum fuels with renewable biofuels has drawn significant public interest. Many states have imposed biodiesel mandates or incentives to use commercial biodiesel blends. We present an inquiry-driven experiment where students are given the tasks to gather samples, develop analytical methods using various instrumental methods, such as HPLC, [superscript 1]H-NMR, and ATR-FTIR, make measurements, and analyze the results to determine the volume percent of biodiesel in commercial diesel blends. The project develops students' appreciation of the usefulness of chemistry by working with "real" samples from their daily lives, and skills to critically compare and contrast the strengths and weaknesses of various instrumental techniques for quantitative analysis. (Contains 1 table and 4 figures.)