Previous literature has documented the repellent properties of catnip (Nepeta cataria) and Osage orange (Maclura pomiferia) essential oils to several insect species. More recently, these essential oils and some of their individual components were shown to have activity against mosquitoes. Studies conducted by the Pesticide Toxicology Laboratory at Iowa State University focus on characterizing mosquito repellency essential oils and have developed mixtures containing different spatial and contact repellent activities. Mixtures consisting of catnip and Osage orange essential oils, and elemol, a sesquiterpene found in the Osage orange essential oil, were evaluated in a laboratory static-air bioassay with several mosquito species. Two new essential oils, Amyris (Amyris balsamifera) and siam wood (Fokienia hodginsii), were also found to have high residual repellent activity. All mixtures containing both contact and spatial repellents showed significantly higher levels mosquito repellency as compared to the individual oils. Studies with solid-phase microextraction sampling inside the static-air chamber provide support for the differences in spatial and contact repellency. Trends observed in repellency screening trials regarding structure-activity and optimization of repellent blends, including residual control, will be discussed.