In 2004, the U.S. EPA estimated that as many as 45,000 former manufactured gas plants (FMGPs) required remediation of contaminated soil or groundwater. The primary contaminants at these sites are tars. FMGP tars are complex, dense nonaqueous phase liquids (DNAPLs), containing several thousand compounds including polycyclic aromatic hydrocarbons (PAHs). PAHs are sparingly soluble, but can dissolve from tars into groundwater at concentrations that exceed levels of concern. Tar DNAPLs can also sink below the water table and slowly migrate underground to impact waterbodies directly. Laboratory studies were conducted to investigate in-situ remediation methods that rely on physical and chemical means. Specifically, column studies were used to evaluate cosolvent flushing for removing PAHs from contaminated soil excavated from an FMGP in Salisbury, NC. These experiments were conducted at varying length scales, ranging from 11.9 to 110 cm. PAH effluent concentrations were modeled using a common two-site sorption model. Fitted mass-transfer rates were two to three orders of magnitude lower than predicted values based on published data. Laboratory studies were also conducted to determine how tar density and viscosity vary as a function of composition and temperature. For this work, samples of tars were obtained from wells at two FMGPs: one in Baltimore, MD and one in Portland, ME. The tar composition varied spatially across both sites. Empirical relationships were developed that can be used in predicting tar recovery during thermal remediation.