Methane (CH4) emission from ruminant livestock, the single most important anthropogenic source of emissions of this gas, has both environmental and nutritional implications. Methane emissions can be accurately measured using enclosure facilities, but if data are to be extrapolated to production situations, caution needs to be exercised as there are limitations. The sulphur hexafluoride (SF6) tracer technique for estimating CH4 emissions exploits the knowledge that most of CH4 is excreted at the mouth and nostrils of the animal. Estimations are based on known release rate of SF6 from a permeation tube introduced into the reticulorumen of an animal and the ratio of CH4/SF6 concentrations in aliquots of excreted gases sampled unobtrusively. The technique remains the method of choice for emission estimations in conditions being similar to those under production. Nevertheless, the accuracy and precision of the technique has been debated. Most of the evaluations of the tracer technique involving sheep and cattle indicate that it agrees well with the respiration chamber methods in their overall mean emission estimates, but a greater variation for SF6 tracer emission estimates remains a common feature. Growing evidence suggests that the large variability of tracer-based CH4 emission estimates is related to the experimental conditions and improper handling of the technique (e.g. inaccurate assessment of background SF6 and CH4 concentrations), and more recently the instability of the sample flow rate has been associated with inaccuracy and imprecision of the technique. Fortunately, the identified and suspected sources of variation are controllable. Here, we discuss some potential issues related to the technique and recommend measures of quality assurance and control when applying the technique.