Gamma-butyrolactone (“GBL”) and Gamma-hydroxybutyrate (“GHB”) having a unique carbon footprint as defined by the percent modern carbon (pmc) are described herein. The percent modern carbon can be controlled by varying the amounts of biobased, renewable starting materials and petroleum-based starting materials to prepare GBL or GHB having a defined pmc or by preparing mixtures of GBL or GHB prepared from biobased renewable starting materials and GBL or GHB prepared from petroleum-based starting materials.