The Working Group of the Biomass Gasification Task of the International Energy Agency (IEA) Bioenergy Agreement has developed a protocol for sampling and analysis of tar and particulates from biomass gasifiers, which is commonly accepted as a standard for reliable measurement of tar in producer gas. The methodology is dependent upon dissolving tar in a solvent for subsequent recovery by evaporation or distillation. This paper investigates whether storage of the tar/solvent sample prior to analysis affects the accuracy of the tar measurement. On the basis of the results of this study, we recommend that samples be analyzed within a few hours of collection and never be stored longer than 24 h.