A small-perturbation semianalytical solution is derived for solute transport in porous media with multiple spatially variable reaction processes. Specific reactions of interest include reversible sorption, reversible mass transfer, and irreversible transformation (such as radioactive decay, hydrolysis reactions with fixed pH, and biodegradation). Laplace transform is employed to eliminate the time derivatives in the linear transport equations, and the transformed equations are solved analytically. The transient solution is ultimately obtained by use of an efficient quotient-difference inversion algorithm. Results indicate that spatial variation of transformation constants for the solution phase and the sorbed phases decreases the global rate of mass loss and enhances solute transport. If the sorbed-phase transformation constant is spatially uniform but not zero, a similar effect is observed when there is spatial variation of the equilibrium sorption coefficient. The global rate of mass loss and apparent retardation are decreased when the spatial variability of the sorbed-phase transformation constant is positively correlated with the spatial variability of the equilibrium sorption coefficient and increased for a negative correlation. ¿ American Geophysical Union 1996