Whoever said “there’s plenty of room for everyone on the Internet” was wrong – at least if you’re looking for advertisement space for your political campaign.

“There’s a finite amount of inventory on premium video sites like on YouTube or Hulu,” says New York Times reporter Ashley Parker.

There are two types of online video ads, and they are priced differently. Skip-able ads give you the option to skip the ad onto the music video or clip that you went on the Internet to watch in the first place. But these are also usually… skipped.

“Those ads do not sell out, but they are sold via an auction system,” says Parker. “Closer to Election Day more people are demanding them, so the price goes up.”

The other type of ad is called “reserved by ads.” These are normally 15 to 30 seconds long.

“Those are more expensive, often, but they can be reserved in advance which is a big advantage for campaigns that think ahead,” says Parker.