Ansari-Lari et al¹ reported that the sex ratio (proportion male) of offspring of men exposed to petroleum fuel is significantly low as contrasted with controls. If confirmed, this is an important result. It is in contrast with reports of significantly high offspring sex ratios in communities exposed to active seepages of natural gas and oil² and to petrochemical air pollution.³ Ansari-Lari et al¹ suggested that this is because in those communities the mothers (as well as the fathers) were exposed. This suggestion is reminiscent of (but not entirely similar to) the data of Mocarelli et al⁴ who reported that men (but not women in the absence of paternal exposure) exposed to dioxin subsequently produce excesses of daughters. In accordance with my hypothesis,⁵ such men reportedly have low testosterone/gonadotrophin ratios.⁶ This being so, I suggest that the hormone concentrations of the male gas station workers of Ansari-Lari et al¹ should be assayed. I predict that these men will also have low testosterone/gonadotrophin ratios. Indeed, the hormone levels and offspring sex ratios of male and female gas station attendants elsewhere should be generally examined. The offspring sex ratio of professional drivers is also reportedly low⁷: the cause (ex hypothesi mediated by low testosterone/gonadotrophin ratios) may also be exposure to petroleum fuel.