The thermal conductivity (k) probe is derived from an idealized transient heat transfer model; therefore, there are inevitable differences between the real probe and the theoretical model. However the k probe is still an accurate and practical measurement device with wide-ranging applications if designed and used properly. Users of a thermal conductivity probe must be aware of its limitations and the possible errors that can develop in its application. This paper includes a theoretical derivation of the k probe equation and some experimental and theoretical simulations of parameters that can cause errors in the application of the k probe. An explanation is given of the significance of certain design and operating parameters. Some of the findings in the study are that the time-correction factor is not required and contact resistance does not affect accuracy. The calibration factor is necessary since it compensates for the difference in the thermal masses of the probe and the sample. Errors due to edge effects and convection can be avoided by limiting data analysis to the linear section of the time-temperature plot. The truncation error is minimized by making beta as small as possible.