Energy and carbon accounting to compare bioenergy crops

► Comparing biofuel crops is exceedingly difficult using conventional measurement methods. ► The PETRO approach quantitatively compares biological matter in terms of energy and carbon. ► Tracking carbon flux from air to liquid fuel compares all biofuel crop yields on a common basis. ► Reporting energy yields (GJ ha−1 y−1) and carbon flux (MgC ha−1 y−1) enables regional comparison.