This paper studies the incidence, determinants and pricing of unprotected oral sex in the London sex services market. The analysis is based upon matched sex worker-client panel data, which were collected from "field reports" on PunterNet.com website over the 1999- 2009 time period. We find a steady increase in the incidence of unprotected oral sex during this period, rising from less than 20% to over 50% of all transactions. We show that the average premium for unprotected oral sex amounts to about 10-14% of the transaction price, and that this premium is higher if a sex worker has agency affiliation. Agency affiliated sex workers are also less likely to engage in unprotected oral sex compared to independent sex workers.