This morning the IAB reported that Q3 US online ad revenue came in at $9.3 billion. First half digital revenues were $17 billion. It's quite possible that the second half will see $19 or $20 billion total, bringing FY 2012 to $36 or $37 billion in online ad revenue (including mobile). However the IAB didn't provide a detailed breakdown of Q3 revenues by segment.
Two days ago eMarketer revised its mobile ad forecast upward for 2012 from $2.61 billion to just over $4 billion.
The IAB said that mobile advertising revenue was $1.2 billion for the first half. It also said that mobile represented 8% of Q2 2012 revenues, or $661 million. While mobile is the fastest growing digital ad segment it's still small relatively speaking. If mobile continued to represent 8% of digital ad revenue in Q3 that would translate into $744 million.
However if mobile grew as a percentage of overall digital revenue to, say, 10% that would represent $930 million in revenue. That's probably the range that's reasonable to assume: $744 to $930 million. Let's take the midpoint of that: $830 million.
Because of the holiday shopping activity surrounding mobile devices we can assume that mobile ad revenue will grow further in Q4. Accordingly, it's possible that Q4 US mobile ad revenues might reach or slighly exceed $1 billion.
We can probably expect mobile ad revenues to come in for the full year between $2.6 and $3 billion on the high end. It's very unlikely that they will reach $4 billion this year however.