Ourinhos Airport (OUS) is a general-aviation aerodrome in the interior of Sao Paulo state, not a commercial passenger airport, so the honest answer is that it has no lounge, no scheduled airline counters, and no passenger terminal in the sense a commercial flyer would expect. It exists for flight training, agricultural aviation, and private or charter aircraft rather than for anyone connecting through on a scheduled flight.
Because Ourinhos sees no scheduled airline service, none of the usual lounge access questions, card networks, airline status, or day passes, really apply here. Pilots, flight students, and private aircraft operators are the airfield's typical users, and the small building on site functions as an operations office rather than anything resembling a passenger lounge. If you are researching Ourinhos because of a private charter or a flying lesson, expect a working aerodrome rather than any commercial-airport amenities. Visiting pilots typically arrange fuel, parking, and any ground handling directly with the aerodrome's operators in advance, another sign that this is a working general-aviation airfield rather than a commercial gateway built around passenger flow.
For a genuine lounge experience in the region, Sao Paulo's real air hubs are the destination to think about instead. Guarulhos International Airport, Brazil's busiest, carries a proper mix of premium options, including pay-per-use spaces such as Plaza Premium Lounge, alongside airline and card-network lounges for eligible travellers. Congonhas, the city's domestic hub, has its own smaller set of airline lounges for premium and elite passengers. Either is a realistic starting point if your trip includes Ourinhos as a private-aviation stop but a commercial flight elsewhere in your journey.
If your itinerary combines a small-aircraft leg through Ourinhos with a commercial flight, plan your lounge visit around Guarulhos or Congonhas instead, and confirm current access terms with your card issuer or airline before you travel. Agricultural aviation activity around Ourinhos also tends to follow the state's planting calendar, which can affect airfield traffic without ever touching passenger amenities.