What do the Expedia PPC agreement and the Kayak acquistion of Sidestep have in common?

Two stories from late 2007 and early 2008 signal a shift in the online travel model. In November 2007 at the PhoCusWright conference in Orlando, Expedia announced a new agreement with IHG that included a pay per click (PPC) compensation model. The acquisition of SideStep by Kayak this month is another significant development. How are these two announcements related? The Kayak/Sidestep merger is a clear validation of the referral model, but also demonstrates the need for scale to be an online travel player globally. The Expedia PPC contract element reflects the simple fact that many people shop OTAs and end up buying at supplier sites a phenomenon that has been validated by PhoCusWright and Forrester research. For Expedia, being paid for referrals represents a new and important revenue stream. You then add Travel 2.0 players such as Farecast, Kango and the Nile Guide, and the value of search and travel planning tools represents a major growth area for online travel here in the US and globally. As the economy softens the value of the referral model is likely to increase as suppliers scramble to fill airline seats and hotel beds.