Before you use shaving oil, you'll first want to wash and clean your face. Otherwise, you'll be placing a layer of oil over a preexisting layer of dirt, dead skin cells and your skin's natural oils. This is going to both make for a poor shave and cause your skin to break out due to clogged pores.
Newer shaving oils contain many ingredients found in moisturizers, including vitamin E, mineral oil, aloe and any number of natural oils, such as avocado oil and sunflower oil. What shaving oil often lacks, however, is the sunscreen that many moisturizers contain. Also, you likely won't find antioxidants that help repair existing skin damage, or vitamin A to stimulate collagen production to help fill in wrinkles.
Shaving oil does moisturize your skin. However, nothing beats actual moisturizer. Though you've applied shaving oil, you've also put the blade to your face, put your hands all over your face, rinsed your face and towel-dried your face. It's a safe bet that a little additional moisturizer -- following a final post-shave cleansing -- could deliver the skincare goods to your face better than whatever remains of the oil you've already applied.
An additional moisturizer is also a better alternative than most aftershave products, which are generally alcohol-based. While the resultant sting and burn of aftershave will make you feel like something is happening (namely an application of antiseptic to your possibly nicked-up skin), what you'll also be doing is drying out your face. After what you've just put your face through, it deserves a little additional moisturizer.
You can also use another "home-remedy moisturizer" that doubles as shaving oil: olive oil. While it won't provide sun protection, a little (high-grade) olive oil can both give your skin a healthier appearance and prevent your razor from removing something that was supposed to remain attached.
See the next page for lots more information on shaving and moisturizers.