If you're the type who spends a lot of time outdoors (no matter what season) or who can't get enough of the beach every summer, you may want to try a sweat-resistant, water-resistant or waterproof sunscreen.
Despite being called waterproof or water-resistant, these products aren't truly waterproof. You're not protected all day long if you've been swimming or sweating outdoors. A product is considered waterproof if it continues to protect you after you've been in water (or if you've been sweating) for an estimated 80 minutes, and water-resistant if it continues to protect you from damaging rays after an estimated 40 minutes. Remember to reapply your sunscreen head to toe every two hours and reapply after vigorous activity or as soon as you're out of the water.
One complaint about waterproof sun blocks is that they sometimes have a tendency to make skin feel dry. This is because they create a barrier to keep from washing off, and also often contain some alcohol so that they dry quickly after applying. While this is less likely to be an issue for oily skin, you still want to be careful about over-drying.