• by Tyler Loechner , Staff Writer @mp_tyler, June 4, 2013

The real-time bidding (RTB) marketplace had a mixed month in May, both globally and in the United States, according to data from Rubicon Project's real-time marketplace app. On the global scale, spend was up 7% but impressions were down 7%. In the U.S., spend increased 10%, but just like the rest of the globe, impressions were down (8%).

The top 5 spenders had a newcomer, with Food & Drink squeezing its way into 5th. Technology & Computing, Automotive, Personal Finance, and Shopping all remained in the top 5, as they have for the last year, while Travel was bumped out for the first time since December 2012.

Overall, advertisers had a strong month when it came to estimated cost per mile (eCPM). eCPM in the U.S. (+20%) outpaced the globe (+15%), but both figures are encouraging. Education and Real Estate were knocked out of the top 5 in terms of eCPM and were replaced by Hobbies & Interests and Religion & Spirituality.

Hobbies & Interests was in the eCPM top 5 for the first time in at least a year. In fact, in the last 12 months, prior to its second place May ranking, the highest ranking the category had achieved was 18th. It has hovered right around 20th in eCPM in each of the last 12 months, so its leap to second is notable.

So, how did Hobbies & Interests achieve this? It wasn't by accident, according to the numbers. The category had the highest percent increase in spend (109%) compared to April among all categories. At the other end of the spectrum, Careers had the biggest decrease in spend, dropping 41%.

Shopping was unable to regain its footing in eCPM after April marked the first time the category didn't appear in the top 5 in nine months. Shopping was 9th in eCPM in May, its lowest ranking in a year. Even though the category slipped when compared to others, Shopping did still have a 15% increase in eCPM compared to its own April numbers.

Looking at eCPM across all categories, only Pets had a decrease (-5%). Education remained at 0% change from April, while all 19 other categories had an increase, with Hobbies & Interests leading the way (186%).

Food & Drink managed to grab a spot in the top 5 for impressions, the first time it has done so in over a year. While Automotive has been in the top 5 impressions every month for the last year, May marked the first time it was in the top 2 since July 2012.

After ranking second behind News every month since Rubicon started tracking back in January 2012, Arts & Entertainment was finally top dog among publisher verticals. News, Education, Sports, and Business rounded out the top 5 May publisher verticals.

May was a decent month for the RTB market. While it was good to see spend increase by 10%, an 8% drop in impressions can't make too many people happy. However, the strong eCPM numbers - both globally and in the U.S. - should be reassuring.