This research project compared the results from a public opinion survey about transportation taxes that was administered using two different survey modes, a national, random-digit-dial (RDD) telephone survey and an online survey with respondents recruited from a panel. There is considerable interest among survey researchers in using online survey panels as a replacement for RDD surveys. RDD surveys are becoming much more expensive to conduct, and researchers also worry that the quality of the results may be dropping because of rising refusal rates for phone surveys. However, a key question for researchers is to understand how a study’s results may differ depending on the survey mode. The survey questionnaire tested for this study asked United States residents their views on various transportation tax and fee options available at the federal level, including questions specifically designed to assess public-transit-related spending. The revenue tools explored include raising the federal gas tax rate and replacing the gas tax with a mileage fee. In addition, the survey collected data on standard sociodemographic variables, a few travel-related characteristics, opinions about the transportation system, and knowledge about funding for public transit. Comparing the results from the two survey modes reveals statistically significant differences both about who answered the survey as well as how respondents answered the questions. Responses were statistically significantly different by survey mode for most questions, with the magnitude of the differences often ten percentage points or more.