  Proton-proton total cross sections are measured with present day high energy
colliders up to 2 TeV in the centre-of-mass of the system (10^{15}) eV in the
laboratory). Several parameterizations, very succesful at low energies, can
then be used to extrapolate the measured values and get estimations of cross
sections to higher energies (10^{17} eV). On the other hand, from very high
energetic cosmic rays (> 10^{17} eV) and using some approximations, it is
possible to get a value for proton-proton total cross section from the
knowledge of the proton-proton total cross section at these energies. Here we
use a phenomenological model to estimate proton-proton total cross section at
cosmic ray energies. On the basis of regression analysis we show that the
predictions are highly sensitive to the employed data for extrapolation. Using
data at 1.8 TeV our extrapolations for proton-proton total cross section are
incompatible with most of cosmic ray results
