If pressure is low it can be rings. Or you have a valve not seating correctly. If a valve is not sealing correctly it will allow compression bypass but it will put the compression in the intake or exhaust. If you have a cylinder testing low on compression spray some penetrating oil in spark plug hole and test again. If compression is much higher the rings are worn. (The oil seals the rings). You can also have a leak down test done and it will test the rings and valves at the same time. It requires a leak down test that a good shop will have but are kinda expensive.