The Search Engine Marketing Professional Organization (SEMPO) estimates that search engine marketing (SEM) will total $13.5 billion for 2008. This number is down from an estimate of $15.7 billion made early last year, according to SEMPO's yearly State of Search Engine Marketing study. SEMPO projects that 88% of the $13.5 billion is being spent on paid search advertisements, 11% on natural search engine optimization (SEO) and 1% on SEM technologies including leasing, agency solutions and in-house development, according to the study, conducted by Radar Research.