  We present a summary of the measurements of mass sensitive parameters at the
highest cosmic ray energies done by several experiments. The Xmax distribution
as a function of energy has been measured with fluorescence telescopes by the
HiRes, TA and Auger experiments and with Cherenkov light detectors by Yakutsk.
The <Xmax> or the average mass (<lnA>) has been also inferred using ground
detectors, such as muon and water Cherenkov detectors. We discuss the different
data analyses elaborated by each collaboration in order to extract the relevant
information. Special attention is given to the different approaches used in the
analysis of the data measured by fluorescence detectors in order to take into
account detector biases. We present a careful analysis of the stability and
performance of each analysis. The results of the different experiments will be
compared and the discrepancies or agreements will be quantified.
