A selection of chemical reagents representing acids (HNO3), bases (NaOH) and oxidants (KMnO4 and catalyzed H2O2) was used to pretreat coal in order to enhance its solubility. The relative bioavailability of the solubilized fractions was assessed using bioassay with Pseudomonas putida F1 by monitoring the production of carbon dioxide (CO2). This bioassay has been shown to be an effective tool for quickly determining the biological potential of coal as substrate for the enhanced production of biogenic natural gas. The concentrations of total dissolved organic carbon in the pretreated samples showed that nitric add and sodium hydroxide were the most promising pretreatment agents with up to 14.0% of coal carbon solubilized. However, bioassay results indicated that the coal pretreatment with permanganate at high concentration resulted in the largest fraction of bioavailable solubilized constituents. Approximately 20.0% of the soluble carbon was biochemically converted to CO2 within a period of 14-days, accounting for nearly 1.1% of the total coal carbon. Although high concentrations of nitrate (NO3-) and sodium (Na+) associated with the acid and base pretreatments may have inhibited the activity of the microorganisms during the bioassay, relatively high concentrations of purgeable organic carbon and other readily biodegradable forms support the study's conclusion. (C). 2013 Elsevier B.V. All rights reserved.