The article is focused on the detailed elucidation of fluorescence quenching by charge and/or energy transfer in pi-conjugated polymers. The processes were studied in blends of MDMO-PPV, Tg-PPV, PCDTBT and PCBTDPP with fullerenes PC60BM and PC70BM in chlorobenzene. Fluorescence quenching was evaluated by the Perrin equation for static quenching and quenching sphere radiuses were calculated. These radiuses were found to be the same as the Foster critical distances for resonance energy transfer. It was concluded that energy transfer prevails over charge transfer under the conditions where the donor and acceptor are not in close contact. (C) 2013 Elsevier B.V. All rights reserved.