Due to the impact of online payment on the development of e-commerce, this article seeks to deepen the current understanding about the determinants of online payment method choice. Based on an extensive literature review, we identified perceived trustworthiness of the seller and perceived product uncertainty as major determinants, and we theorize that product type, product price, and product description are antecedents of product uncertainty. In our theoretical framework, we model perceived trustworthiness of the seller and perceived product uncertainty as independent variables, which are hypothesized to predict the dependent variable, namely online payment method choice (credit card, debit card, or cash on delivery). Moreover, we define payment method characteristics (e.g., information security) and buyer characteristics (e.g., trust propensity, online shopping experience) as control variables. Also, we describe a laboratory experiment in which we test our theoretical framework. Considering the recent calls for the use of neurobiological and physiological approaches to advance information systems (IS) theorizing (see, for example, www.NeuroIS.org), we suggest using eye-tracking data to complement traditional data sources, particularly those captured through survey research. Specifically, we propose that eye- tracking data can be used to measure product uncertainty, a major predictor of online payment method choice, which is associated with unconscious and automatic informationprocessing that cannot be articulated easily through self-reports.