Hydraulic fracturing is routinely used to release and produce petroleum from multistacked shale layers. Although it is known that some shale layers are more productive than others, actually allocating produced oil volumes to individual reservoirs is difficult. In this paper, we introduce a new allocation technique that is based on the heterocompounds (nitrogen-, sulfur-, and oxygen-containing) detected by electrospray negative-ion ESI(−) Fourier transform ion cyclotron resonance mass spectrometry. A total of 2 oils and 5 mixtures thereof prepared in the laboratory, 4 produced oils and 2 shale bitumens extracted from the Vaca Muerta Formation (Argentina), and 5 produced oils and 15 shale bitumens extracted from the Niobrara Formation were used to test and illustrate the utility of the newly developed technique. The allocation results show a good match to conventional geochemistry indices based on gross polarity fractions, C_27-28-29 diasteranes, pristane, and phytane. The chemostatistic allocation method is capable of deconvoluting the contributions of individual shale layers using bitumen extracts and is not influenced by fractionation. The newly developed allocation technique can assist in the rapid development of multistacked shale reservoirs. Allocating point source or genetic contribution to a conventional oil play is another potential application (i.e., oil-source correlation).