The purpose of this study is to investigate understanding levels of high school students, chemistry student teachers and prospective science teachers on the gas concepts. The sample consists of 107 chemistry student teachers, 141 prospective science teachers and 40 high school students. A test involving 16 questions is used to collect data. The results show that there are significant differences between the means of high school students, the means of chemistry student teachers and prospective science teachers in favor of the high school students and student teachers have alternative conceptions that are similar to those of the high school students. (C) 2013 The Authors. Published by Elsevier Ltd.