An analytical theory is suggested for carrier recombination in organic bulk heterojunction (BHJ) structures taking into account the spatial separation of recombining species. In BHJ systems, electrons and holes are confined to two different material phases, and the nongeminate recombination can happen only at the interfaces between the phases. The carrier concentration in the vicinity of the interface can essentially differ from the average concentration in the bulk. Conditions are considered at which this difference can lead to deviations of the apparent recombination order from the value δ=2 that is generally expected for bimolecular reactions. The theory is universal in the sense that it is based solely on the inhomogeneous distributions of the recombining species. It can therefore be applied not only to organic semiconductors but to any system in which recombining species are confined to different material phases and can meet only at the interfaces between these phases.