Electronic cigarettes (ECIGs) are among the most important issues in public health today due to their dramatic increase in popularity. However, very little is known about ECIGs, including what factors may make them more likely to be used and abused. Examining factors that influence nicotine yield, delivery, and subjective effects from ECIGs is essential to understanding their abuse liability. Limited pre-clinical research has revealed that nicotine yield may be influenced by the ratio of the two liquid vehicles, propylene glycol (PG) and vegetable glycerin (VG), most commonly found in ECIG solutions. Specifically, higher proportions of PG result in greater nicotine yields. However, the influence of PG:VG ratio on nicotine delivery and subjective effects associated with ECIG use has not been examined previously. The primary hypotheses are that higher proportions of PG will result in greater nicotine delivery and subjective effect profiles suggestive of higher abuse liability in ECIG users. Results from this project will result in further understanding of the factors that influence the abuse liability of ECIGs and could inform regulation of these products.