Pharmacokinetic studies are often used to assess the rate and amount of nicotine delivery into the bloodstream during product use. Knowledge about intra-individual and inter-individual variability of pharmacokinetic (PK) parameters is important in the design of PK study for e vapor products (EVPs). We analyzed two plasma nicotine PK parameters, maximum concentration (C_max) and area under the curve (AUC) from three randomized controlled crossover PK studies (n = 27, 36, 38, respectively) in which various commercial and prototype EVPs were used by adult cigarette smokers under two different use conditions. The first condition was a controlled use of 10 inhalations of 4 second duration with 30 second intervals and the second condition was an ad libitum use condition (use for 10 minutes without restrictions on inhalation times and duration). A linear mixed model that included study product, sequence and period as fixed effect and subject as random effect was used to estimate the intra- and inter-individual variability. The average variability (CV %) across the three studies was larger under the ad libitum condition (intra-individual mean = 32.3 % and inter-individual mean = 52.9 % for C_max; intra-individual mean = 26.3 % and inter-individual mean = 54.3 % for AUC) than under the controlled condition (intra-individual mean = 31.6 % and inter-individual mean = 39.3 % for C_max; intra-individual mean = 22.8 % and inter-individual mean = 36.2 % for AUC). The average intra-individual variability across the three studies for C_max and AUC was smaller than the average inter-individual variability under both conditions. In each study, the intra-individual variability for both parameters was smaller than the inter-individual variability. For the ad libitum condition, the inter-individual CV in C_max was 52 %, 52 % and 53 %, respectively in three studies and the inter-individual CV was all around 54 % for AUC in three studies, indicating consistency across studies. These variability estimates can inform design of future EVP PK studies.