An international collaboration was initiated by thirteen different research groups to understand and explain the differences in auto-ignition delay times, measured on different rapid compression machines, RCMs, of different design and size [1,3]. The Consortium measured delay times, k, for ioctane under the same conditions: fixed oxygen content of 21%, pressure at the end of compression, Po, 2.0 MPa, and compression temperatures, To, in the range 650-950K. Figure 1 gives the experimental auto-ignition delay times, ke , from seven different RCMs plotted against 1000/To. Each point is identified by a number unique to each participating group. There is significant scatter in ke , particularly at the intermediate and low temperatures