In an effort to develop a broadly applicable approach to the facile one-pot synthesis of oligosaccharides, the reactivity of a number of p-methylphenyl thioglycoside (STol) donors which are either fully protected or have one hydroxyl group exposed has been quantitatively determined by HPLC. We have characterized and quantified the influence on reactivity of the structural effects of different monosaccharide cores and different protecting groups on each glycoside donor. In addition, we have established a correlation between glycosyl donor reactivity and the chemical shift of the anomeric proton by H-1 NMR. Using the reactivity data, we have created a database of thioglycosides as glycosyl donors and demonstrated its utility in the easy and rapid one-pot assembly of various linear and branched oligosaccharide structures. In addition, we have developed the first computer program, OptiMer, for use as a database search tool and guide for the selection of building blocks for the one-pot assembly of a desired oligosaccharide or a library of individual oligosaccharides.