Nonimmigrant traveler to the U.S. must keep the departure portion of Form I-94 and passport in his/her possession at all times until departing the U.S. If a traveler boards a commercial conveyance (such as airplane) to depart the U.S., the transportation carriers are:

1. To remove the departure portion of the Form I-94 from the traveler's passport.
   
   
2. Annotate the reverse of the departure portion of the Form I-94 with the facts of the applicant's departure from the U.S.
   
   
3. Return the departure portion of the Form I-94 to the nearest CBP office.
   
   

You must make sure that a transportation carrier (such as the airline) personnel collects your departure portion of the Form I-94. If you depart the U.S. by way of land through Canada or Mexico, it is your responsibility to return the departure portion of the Form I-94 to a Canadian or Mexican immigration officer upon departing the U.S. If you are departing by ship, submit Form I-94 to the ship representative.

Taking these measures proves that you have not stayed in the U.S. beyond the authorized period, you didn't violate U.S. laws by staying longer than approved, you obeyed U.S. immigration laws, all of which are essential if you want to return to the U.S. at a future date as an immigrant or nonimmigrant.

If you didn't submit the Form I-94 or it was accidentally not collected, here is how you should  return the I-94 to CBP.

Effective May 6, 2007, international visitors will no longer be required to use the US-VISIT exit kiosks when they leave the United States.