Coal and gas outburst is a serious coal and rock dynamic disaster, and effective prediction is essential to control. The initial expansion energy of released gas (IEERG) is a new method to predict coal and gas outburst, which depends primarily on the gas pressure and degree of coal fragmentation. The IEERG reflects the effects of the ground stress, the gas pressure, and coal strength on the coal and gas outburst. On the basis of the single factor on the IEERG, three factors have been studied by orthogonal experiments, including gas pressure, coal particle size, and moisture. The results show that the influence of gas pressure, coal particle size, and water content on the IEERG decreases in turn; that gas expansion energy increases significantly as gas pressure increases; and that the greater the gas pressure, the faster the increase. The index W-p of IEERG first increases and then decreases with an increase in coal particle size and decreases with an increase in moisture content. Through this work, the main influencing factors of gas expansion energy have been defined. This method offers an important theoretical and practical significance to predict coal and gas outbursts. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.