Group Space is offered by many cruise lines. This usually starts at 8 staterooms (double occupancy). Some cruise lines will offer a "group discount" price. Many times you can also get a group amenity when you have at least 8 staterooms. This could be an extra onboard credit, bottle of wine, onboard reception or any number of things, depending on the number of "points" assigned by the cruise line for the group space. Some cruise lines require a small deposit on the rooms until you are able to put the names down, otherwise will allow the travel agent to hold space without a payment until much closer to the cruise. You'll want to use a travel agent that knows the group procedures for the cruise lines you are considering. Group space is not the same on all cruise lines. I definitely have a short list of cruise lines that have the best group policies.