The gelation of a polyvinylalcohol-glutaraldehyde-water solution confined in a Bentheimer sandstone was characterized by carrying out H-1-n.m.r. spin-lattice relaxation rate measurement (1/T-1) and pulse field gradient diffusion (D) measurements at 67 degrees C. At any time during the gel reaction neither the longitudinal magnetization versus storage time nor the echo-amplitude versus gradient strength (squared) could be described by single exponential functions. In order to characterize these multi-exponential decay curves by a minimum number of parameters a gaussian type of distribution function (Rayleigh distribution) in 1/T-1 and D were adopted. When implementing these distribution functions and fitting all spin-lattice relaxation data and diffusion data simultaneously, in order to constrain the fitting more effectively, the two n.m.r. derived parameters (1/T-1 and D) were found to give consistent results. During gelation the average relaxation rate and the average diffusion coefficient versus reaction time were found to be described by a first order rate process with a rate constant equal to 18 X 10(-5) s(-1). Also, the widths of the two distribution functions were found to decrease with reaction time. Moreover, the gelation rate within the Bentheimer sandstone was found to be significantly faster compared to the gelation rate of the bulk solution.