Paid search advertising is a critical source of traffic for sellers on e-commerce platforms. As the mobile Internet gains prominence as the main channel for reaching consumers, sellers need to know how to select and bid on keywords in online versus mobile search settings. This study compares the differential effects of paid search keywords in online and mobile settings on both direct and indirect sales, along with the moderating roles of keyword specificity and keyword cost. Two field studies and two lab experiments consistently show that a paid keyword in a mobile setting can prompt higher direct sales than it does in an online setting, but it generates lower indirect sales in general. Moreover, while keyword cost attenuates this positive relationship between mobile searching and direct sales, keyword specificity and keyword cost attenuate this negative relationship between mobile searching and indirect sales. Empirical evidence also reveals the sales and return on investment of paid search keywords in mobile and online settings. This study enriches previous literature by detailing new insights into the distinct settings of mobile and online search advertising.