The catalyst decomposition in homogeneously catalyzed reactions is a very important factor that has been studied for the oligomerization of n-butenes in a system of two liquid phases. A highly active catalyst [NiCl2( PMe3)(2)] was investigated with an emphasis on the long-term catalyst activity using N-methylpyrrole as a buffer. The recycling experiments indicated that this catalyst is viable for five runs. Furthermore, introducing aluminum chloride or an ionic liquid in small concentrations led to increased stability, though fine adjustments were necessary to arrive at optimal results.