This article aims to assess the adequacy of the existing studies to appraise the compatibility of biodiesel with fuel delivery materials (FDM) under physical diesel engine operation. The existing studies are deemed insufficient to appraise the compatibility of FDM with biodiesel under physical diesel engine operation. This is because the employed standard methods do not replicate the diesel engine operating conditions such as varying fuel pressure/temperature and the presence of FDM which can also influence the FDM degradation rate. Addressing the above, recently published work disseminated the deterioration of biodiesel under common rail type diesel engine operation. From it, the identified FDM degradation factors such as oxidized biodiesel was not detected while the TAN value and water content did not change. Instead, the dissolved oxygen concentration and conductivity value of the biodiesel samples changed significantly. Better compatibility was found present between FDM and biodiesel under novel immersion method which incorporated fuel renewal to mimic biodiesel deterioration under typical engine operation condition contrasting to under typical immersion method. This therefore demonstrates that more works aligned to these recently published works emphasizing on engine operating conditions are critical to conclude on the compatibility of biodiesel with FDM under physical diesel engine operation. (C) 2019 Elsevier Ltd. All rights reserved.