Bullsnake
Pituophis catenifer sayi

Size:  4 1/2 - 6 1/2 ft
Distribution
Statewide, except extreme eastern part of the state.  The bullsnake is Oklahoma's largest snake.  A powerful constrictor, this central plains species of the Pituophis melanoleucus complex is a common "rat snake".  The bullsnake is one of the few snake species capable of creating a loud hiss, which sounds incredibly like the rattle of a rattlesnake.  Like other rat snakes, the bullsnake can inflict painful bites, and are usually prone to bite when first startled or handled.  However, they also habituate quickly.  That is they easily become accustomed to humans and can become quite gentle with a little patience.
*Note: According to Joseph Collins (The Center for North American Herpetology), a 2007 Molecular DNA analysis has joined the American rat snakes, genera Elaphe/Pantherophis, to the genus Pituophis.