The Oxford is meant to be a formal shoe. In today’s era, there are lots of different kinds of Oxford shoes available and can be worn in a more casual manner. A leather Oxford in a brown or black will more often be for work or weddings, perhaps a very fancy date where you plan to propose to a young woman.
If you’re going towards a cheaper Oxford shoe in a funky color, you’ll probably be fine wearing it with jeans. Be careful with this; you may need to watch your shoe color and make sure it would be considered inappropriate for the other kinds of events that an Oxford is typically worn to. Especially if it’s a good leather material, but it’s still cheaper than others.
A pair of classic Oxford shoes can take you anywhere, and from day to evening. But they are no good for the beach! The work in unlacing makes them entirely impractical. They're not much fun for lounging around at home in the evening, either.
Some fashionistas recommend that you steer clear of Oxford shoes when wearing jeans, and that's certainly true of boot cut jeans, but with a slim, well cut pair of jeans the Oxfords will dress it up and make you look stylish, if you also have a well fitting T-shirt.