There is not always a booking agreement, but if there is it exists between you and OBOS. When you sign the agreement, you pay a reservation fee, which is later transferred to the cooperative as part of your advance payment. The booking agreement is not binding. If you change your mind, you can get some of the paid amount back.
The preliminary agreement is the first binding contract between you and the housing cooperative. The preliminary agreement should contain the conditions for the agreement to be valid, for example that a certain number of properties have to be sold before construction can begin. When enough preliminary agreements have been signed and the financing and planning permission are in place, the cooperative can enter into the agreements with OBOS and others (management organisation and so on) which are necessary to carry out the project.
The agreement on the lease of tenancy rights, to give it its full name, exists between you and your housing cooperative. When the board accepts you as a member of the housing cooperative you have signed an agreement with, you formally become the tenant-owner.
If at a later date you decide to sell your tenant-owner property, you make a formal transfer. This is why the agreement in this situation is called a transfer agreement, i.e. it is different to the initial lease signed with a new private housing cooperative.
The transfer agreement is usually an agreement between private individuals, and must always be made in writing. Also bear in mind that the board must accept the new buyer as a member of the housing cooperative for the transfer to go through. There are clear rules on what information must be included in a transfer agreement, which you can ask your estate agent about.