Objective: Nicotine concentration, form (salt vs. freebase), and type (synthetic vs. tobacco-derived) are key characteristics of e-cigarettes that manufacturers manipulate. Marketing claims such as "tobacco-free" may attract new consumers and increase product use intentions. This study aimed to monitor the nicotine claims of e-cigarettes and assess their market proportions in the U.S. Methods: We analyzed e-cigarette sales and nicotine marketing claims using Nielsen ScanTrack data from U.S. brick-and-mortar stores. Market proportion was calculated as the ratio of unit sales of each nicotine claim category to the total unit sales of e-cigarettes between 12/24/2023 and 1/20/2024. Results: Nicotine claims were categorized into six groups, with the following market proportion: nicotine (77 %), nicotine salt (10.1 %), synthetic nicotine (2.2 %), zero tobacco or tobacco-free (2.2 %), zero nicotine or nicotine-free (0.03 %), and no claim (8.7 %). The market proportion of each category of nicotine concentration was as follows (market proportion in parentheses): 0 % (0.04 %), 0.1 to less than 2 % (2.9 %), 2 to less than 5 % (16.2 %), 5 % or higher (73.0 %), and unspecified (7.9 %). Conclusions: The market proportion of products that explicitly used nicotine salt, synthetic nicotine, or tobacco-free claims was notable. Products with high nicotine concentration (5 % or higher) dominated the market, highlighting their continued popularity.