Second-Price Auction Specifics

Google's generally a second-price auction. So each spot higher in the order is more expensive.
Mr. Hurst[5]
In a first-price auction, an auction winner will be charged exactly what they had submitted as their bid.
THE WITNESS[1]
In contrast, within a second-price auction, an advertiser is not necessarily charged exactly what they bid.
THE WITNESS[1]
The amount that we charge an advertiser is the least that they hypothetically could have bid while still receiving their allocation.
THE WITNESS[1]
Google uses a second-price auction for search text ads because we consider it to be a more advertiser-friendly auction mechanism.
DR. JUDA[1]