Immigration and Nationality Act §212(a)(9)(B)(i):
Under §212(a)(9)(B)(i) of the Immigration and Nationality Act (INA), an alien who is unlawfully present in the US for a period of 180 days but less than 1 year, and leaves the US prior to the commencement of proceedings is unable to return to the US for 3 years. If an alien is unlawfully present in the US for more than 1 year or more, and leaves the US, he or she cannot seek admission within 10 years of the date of departure or removal from the US.
http://bogota.usembassy.gov/scs22a9b.html
Under §212(a)(9)(B)(i) of the Immigration and Nationality Act (INA), an alien who is unlawfully present in the US for a period of 180 days but less than 1 year, and leaves the US prior to the commencement of proceedings is unable to return to the US for 3 years. If an alien is unlawfully present in the US for more than 1 year or more, and leaves the US, he or she cannot seek admission within 10 years of the date of departure or removal from the US.
http://bogota.usembassy.gov/scs22a9b.html