Cats outnumbered dogs by millions as house pets in USA. In USA alone, there are about sixty million cats kept as pets. There are about five hundred million pet cats in the world. There are about forty different species of wild cat. The life span of a pet cat varies from about fifteen to twenty years but some pet cats live for more than thirty years. Neutered cats live longer than non neutered ones, partly because they have less desire to roam. Cats Welfare is a site that offers this information as well as information regarding general health concerns, feeding, breeding, and social interaction.