Nitroxide-mediated polymerization of styrene using 2,2,6,6,-tetramethyl-1-(1-phenyl-ethoxy)piperidine ( 1, styryl-TEMPO) as initiator/ regulator in the presence of an additional more efficient alkoxyamine is presented. Sterically highly hindered alkoxyamines such as 2,6-bis(tert-butyldimethylsilanyloxymethyl)-2,6-diethyl-1-(1-phenylethoxy) piperidine (5, J. Am. Chem. Soc. 2003, 125, 16327), 2,2,6,6-tetraethyl-4-methoxy- 1( 1-phenylethoxy) piperidine (6, Chem. Eur. J. 2004, 10, 1156), and the open-chain alkoxyamine N-tert-butyl-N( 2-methyl-1-phenylpropyl)-O-(1-phenylethyl) hydroxylamine (3, styryl-TIPNO, J. Am. Chem. Soc. 1999, 121, 3904) were used as additives in these studies. The polymerization can be accelerated by a factor of 2 with efficient alkoxyamines as additives. The best results were obtained with 6. The efficiency of an alkoxyamine acting as an additive correlates with the equilibrium constant between the alkoxyamine and the styryl radical and nitroxide. Good results are obtained using additive concentrations as low as 20% with respect to styryl-TEMPO. Molecular weight distribution remains narrow. The results are further supported by numerical simulations.