How do I reserve multiple rooms on Marriott.com?

For one to three rooms:
Our online reservation system will allow you to book three rooms at a time per reservation. Simply choose 1, 2 or 3 from the “Rooms” dropdown menu when starting your search.

For four to nine rooms:
You may reserve up to three rooms at once online. To reserve four to nine rooms, first make a reservation of three rooms and then choose “Book more rooms at this hotel” at the top of the screen, below the confirmation number, when you complete your first reservation. This will save the hotel name, your travel dates, address and credit card information so you can easily make one or more additional reservations.

You may also choose to book 4-9 rooms at once over the phone with a reservation agent by calling your local Worldwide Reservations Telephone Number.