As of 2023, Elfbar remains the most popular brand of disposable e-cigarette available in the United States (US) and United Kingdom (UK), with similar flavor options in both countries. At the time of this study, 5% nicotine Elfbar BC5000 was the only version available in the US, whereas 2% Elfbar 600 was the most popular in the UK. This study measured differences in nicotine content and form, aerosol emissions and flavoring chemicals in the US and UK Elfbar products. A convenience sample of eight Elfbar devices sold in the US and UK, consisting of two Elfbar models with four identical flavor options (Peach Ice, Strawberry Banana, Strawberry Ice and Strawberry Kiwi) purchased between December 2022 and February 2023, were laboratory tested. We measured nicotine concentration, form and total content. We also determined aerosol emissions and estimated the nicotine dose delivery per puff. We identified solvents and flavoring chemicals in these products. Elfbar products within the same country had similar nicotine content, concentration, form and solvents, but they differed in flavoring chemicals. US Elfbar contained, on average, higher volume (mean ± standard deviation = 6.5 ± 0.5 versus 1.8 ± 0.3ml) of nicotine solution with a higher concentration (41.8 ± 2.3 versus 19.7 ± 1.2mg/ml) than the UK Elfbar. An estimated dose of nicotine delivered per puff was four times higher from US Elfbar than UK Elfbar. There were differences in the type and amount of flavoring chemicals used in US and UK Elfbars, including a higher concentration of a synthetic coolant WS-23 in US Elfbar than in UK Elfbar (17.8 ± 1.5 versus 12.9 ± 5.4mg/ml). Because the amount of nicotine found in the US Elfbar e-cigarettes is equivalent to that found in eight UK Elfbar e-cigarettes, people who use Elfbar sold in the US have access to much more nicotine from a single device than those who use Elfbar sold in the United Kingdom.