Reversible leaching of palladium nanoparticles occurs in a variety of catalytic reactions including cross-couplings, amination, the Heck reaction, etc. It is complemented by capturing of soluble palladium species on the surface of nanoparticles and de novo formation of nanoparticles from Pd precatalysts. We report here a detailed computational study of leaching/capture pathways and analysis of related stabilization energies. We demonstrate the validity of the "cocktail-of-species" model for the description of Pd catalysts in ArX oxidative-addition-dependent reactions. Three pools of Pd species were evaluated, including (1) the pool of catalytically active Pd nanoparticles with a high concentration of surface defects, (2) the pool of monomeric and oligomeric L[ArPdX] _n L species, and (3) the pool of irreversibly deactivated Pd. Stabilization by ArX oxidative addition, coordination of base species, and binding of X ^- anions were found to be crucial for "cocktail"-type systems, and the corresponding reaction energies were estimated. An inherent process of ArX homocoupling, leading to the formation of Pd halides that require reactivation, was considered as well. The pool of irreversibly deactivated Pd comprises nanoparticles with (1»1»1) and (1»0»0) facets and Pd in the bulk form. The study is based on DFT modeling and specifies the role of Pd nanoparticles in (quasi-)homogeneous coupling reactions involving ArX reagents.