Leopard geckos are temperature-sexed, meaning that the gender of the offspring will vary with the temperature you've incubated them at. As far as I know (and I don't breed! so you might want to ask someone else for further clarification), higher temperatures result in males, while cooler temperatures produce females. There are some rare cases, however, of males hatching amongst hatchlings incubated for females (called "cool males I believe), and females hatching amongst hatchlings incubated for males (called "hot females).
