Imperfect consumer price information gives sellers market power. We study how this shapes tax pass-through. In a consumer search model, pass-through rises with the share of consumers who know all prices and is higher for the lowest price in a market, paid by informed consumers, than for the average price, paid by uninformed consumers. Pass-through to the average price is nonmonotonic in the number of sellers, whereas the pass-through gap between the two prices widens with it. Five tax changes in German and French fuel markets support these predictions, comparing fuel types with differently informed buyers within the same stations.