What’s the difference between parts labeled as OE, OEM, OES, and Aftermarket?

There is often confusion between these terms and some important distinctions should be made when vendors use them in reference to parts. If the following definitions are still vague, see the analogy at the end.

OE (Original Equipment): The Genuine BMW part

This is the exact same part you would receive at a dealership with the BMW logo present. Parts are manufactured by a number of companies to meet BMW’s standards, and are branded as Genuine BMW to be used and sold by BMW. For the entire automobile (excluding the replacement of worn parts), Original BMW parts carry a warranty of two years regardless of the mileage.

BMW Parts Warranty: http://www.bmw.com/com/en/owners/service/warranty.html

OEM (Original Equipment Manufacturer): From a manufacturer of any Genuine BMW part

When used in online forums, OEM is generally used and understood to be synonymous with OES (below). When purchasing parts online, however, OEM can sometimes be used to note a higher level of quality, and it may or may not mean OES, depending on the vendor's interpretation. Reason to be aware of the difference, is that some parts vendors don't always use these terms the same way and list OEM and OES separately.

When the same company differentiates between OEM and OES, this part can be made by a company that manufactures and supplies a Genuine BMW part. These parts are sold from the manufacturer directly to suppliers and retailers, as opposed to through the dealer network. Parts from the manufacturer may or may not be used by BMW, but are of higher quality and can often be had for a much lower price.

OES (Original Equipment Supplier): From the manufacturer of that specific Genuine BMW part

When the same vendor lists this separate from OEM, the company that makes this part is the same company that supplies it to BMW. A company may manufacture a dozen parts but only be the supplier to BMW for one of them. Parts labeled as OES are the ones that ultimately become the Genuine BMW part, and usually have the BMW logo ground off if purchased outside the dealer network. All other parts the company makes that aren’t supplied to BMW can be referred to as OEM in this instance.

Again, when used in online forums, OEM is generally used and understood to be synonymous with OES, but some parts vendors are known to use these terms differently. So, depending on where you buy online, it's safer to assume that OES is always OEM and OEM is not always OES. When used in online forums, they are typically one and the same.

Here’s a quick analogy to help better visualize the differences above:

I own a small bakery that sells pastries and desserts to local restaurants, as well as to walk-in customers.

If you’re out to dinner at a restaurant and order a slice of pie, I originally made it and sold it to the restaurant, and the restaurant resells it as theirs. This is an OE Genuine restaurant piece of pie with the restaurant’s name and reputation associated with it (at the restaurant’s higher price).

If you go down the street to my bakery, you can buy that same slice of pie directly from me, made with the same ingredients and from the same oven. This is an OES piece of pie since it’s the exact same pie I supply to the restaurant (I’m also able to sell it at a lower price).

While you’re in my store, you might want to try a piece of cake, as well. This is an OEM piece of cake, because I don’t supply it to the restaurant like I do the pie. As a customer, you would hope that if I make good pie, I would make good cake. I would like to think so, too, but the restaurant may prefer cake from another source (better quality, more cost efficient, etc.), so the pie is referred to as OES, and the cake, along with everything else I sell, is OEM.

This same analogy can be applied for all the other items used in the restaurant’s menu.

As far as aftermarket goes, that’s another bakery opening up that doesn’t supply deserts to the restaurant whatsoever. The bakery may use poor ingredients or they may use superior ones. Either way, they don’t supply anything to the restaurant so are neither OES nor OEM.