Compartments are how OCI organises resources, and they are also the most reliable ownership signal in your cost data. Every resource lives in exactly one, and the compartment is recorded on every cost line.
Design for the questions you will ask
A compartment tree can be organised by team, by environment, by application, or by a mix. There is no universal answer, but there is a useful test: for each of your regular cost questions, can you answer it by looking at one branch of the tree?
A common, workable pattern
•A top level that reflects the organisation, such as a business unit or product area.
•Beneath it, a level for the application or project.
•Beneath that, a split by environment, such as production and non-production.
Keep shared platform services, such as networking and security tooling, in their own compartments. Their cost belongs to everyone, and mixing it into one team's compartment makes that team look more expensive than it is.
Pitfalls
Too deep.: A very deep tree is hard to read in reports and hard to keep tidy. A few levels is usually enough.
Environment only in the name.: If the environment is only implied by a compartment name, filtering is fragile. Back it up with a tag.
Moving resources.: Moving a resource between compartments changes where its future cost lands, not where its past cost landed. Plan the structure early.
Compartments and tags work together
Compartments say where something lives. Tags say what it is for. Use compartments for ownership and access control, and tags for the finer detail such as project and cost centre.