Honestly, oiling a wooden park bench will absolutely help it last longer than leaving it bare—but it probably won’t make it outlast a good metal park bench. The real difference often comes down to bench maintenance and what you mean by “last longer.
If you have a wooden park bench made from a rot-resistant species like teak, cedar, or white oak, a penetrating oil treatment for wood once or twice a year can extend its life to 15–25 years. The oil helps the wood shed water, reduces cracking and surface checking, and keeps the grain from drying out. But oil is not a permanent shield. It wears off, needs reapplication, and won’t fully stop rot if the bench sits in standing water or has joints that trap moisture. Untreated pine or cheap softwood may still fail in 5–10 years even with oil.
A metal park bench—especially powder-coated steel or aluminum—is usually the better long-term choice if you want low maintenance. Aluminum won’t rust. Powder-coated steel resists rust until the coating gets scratched, and even then it can be touched up. A good metal bench can last 20–30+ years outside with almost no upkeep, though it may get hot in sun, cold in winter, and may dent or scratch. Cheap uncoated steel is the exception: it can rust badly in a few years.
So my practical advice: if you love the look and warmth of wood, don’t be afraid of it—but buy naturally durable wood, keep it off wet soil, and oil it regularly. If your top priority is outdoor bench durability with minimum effort, buy a quality metal bench, preferably aluminum or powder-coated steel, and you’ll likely get more years for less work.