This paper presents new evidence of asymmetric pass-through, the notion that upward cost shocks are passed through faster than downward cost shocks, in U.S. gasoline prices. Much of the extant literature comes to seemingly contradictory conclusions about the existence and causes of asymmetry, though the differences may be due to different aggregation (both over time and geographic markets) and the use of different price series including crude oil, wholesale, and retail gasoline prices. I utilize a large and detailed dataset to determine where evidence of a passthrough asymmetry exists, and how it depends on the aggregation and price series chosen by the researcher. Using the error correction model, I find evidence of pass-through asymmetry based on spot, rack and retail prices, though the largest effect is found in the rack to retail relationship. I find more asymmetry in branded prices compared with unbranded prices, consistent with a consumer search explanation for asymmetry. However, I also find evidence consistent with explanations based on market power as the magnitude of asymmetry is positively associated with retail concentration. On average, retail prices rise three to four times as fast as they fall.