Positron emission profiling (PEP) has been used to obtain in situ images of the pulses of C-11-labeled alkanes passing through packed beds of acidic zeolites at temperatures typical of the hydroisomerization reaction. Used in this manner, PEP represents an in situ version of tracer pulse chromatography. The two-dimensional activity-position-time profiles measured were fit to an analytical solution. The method of moments was then applied to the subsequent fitted profiles to extract information regarding adsorption and diffusion of the hydrocarbons. Data concerning the mass transfer of alkanes are necessary to perform further modeling of profiles obtained during the hydroisomerization of n-alkanes on Pt/acidic zeolites.