Figure 8. Methane d¹³C versus ethane d¹³C for coalbed gases in Canada, Poland, and the United States. Sources of data are listed in Table 1. Compositional trend for gases generated from oil-prone source rocks with maturation is estimated from James (1983), Sundberg and Bennett (1983), Jenden et al. (1988), and Jenden and Kaplan (1989).