The use of near-infrared spectroscopy (NIRS) for the determination of biogas and/or methane yields is a relatively new application of the technique. The accepted method of measuring the potential yield, the biochemical methane potential (BMP) test, involves the digestion of test substrates in an inoculum sourced from an active biogas reactor. The details of the BMP method vary, despite attempts at standardization. However, all the various methods are time consuming, with digestion times typically in the range of 30-100 days, and they are also rather labor intensive. The use of NIRS to predict gas yields can potentially cut this time to a matter of minutes and can even be implemented as an online measurement. But before NIRS can be used to give a reliable indication of true gas yields, there are many obstacles to be overcome, particularly regarding the uncertainty due to the poor standard error of laboratory of the reference method.