A method is described for measuring the diversity of combinatorial oligonucleotide libraries that entails extrapolating the base composition of a co-synthesized model library (dNC, N = A, C, G, T) to that of a multibase library template. The base composition of dNC was measured by HPLC. The ability of dNC to predict the base composition of a multibase library template was corroborated by measuring the composition of a 12 base combinatorial library. The base composition of the 12 base library was determined by several template dependent incorporation assays: measurement of restriction fragment specific activities from polymerase incorporation/restriction enzyme digests, template directed radionucleotide primer extension and quantitative dideoxynucleotide sequencing. Additionally, a convention for describing oligomeric combinatorial library (OCL) diversity is proposed. The convention uses a quantity termed the diversity quotient (Qd) to describe library breadth and the mole fraction of the least represented monomeric unit of the OCL to calculate minimum library quantity requirements. Similar methods/conventions could presumably be developed/adopted for non-nucleic acid libraries.