Market efficiency is distorted when retailers are unwilling to pass on changes in wholesale costs or the price of oil (as a major production input cost) to motorists. Existing approaches to measuring pass-through parameters may obscure such behaviour because of the use of fixed-parameter models and/or aggregated price data across different locations and brands over time. We contribute to the literature by examining if there is a mismatch between wholesale and retail petrol prices across different brands supplying unleaded petrol within the same geographical location. To do so, we examine the effects of upstream shocks, arising from changes in oil or wholesale petrol prices, on the retail petrol prices of 672 stations in Sydney, Australia's largest city. We find that the pass-through parameters are significantly lower for stations with fewer competitors in their immediate proximity. When there are fewer than 13 petrol stations within a 5-km radius, or 33 stations within 10 km, irrespective of their brand, they become increasingly less responsive to changes in the wholesale petrol price or the price of crude oil. Our findings enhance market transparency and provide regulators with a rule of thumb that allows them to monitor the unleaded petrol market more effectively.

当零售商不愿将批发成本或石油价格（作为主要生产投入成本）的变化转嫁给驾车者时，市场效率就会扭曲。由于使用固定参数模型和/或随着时间的推移跨不同位置和品牌的汇总价格数据，现有的测量传递参数的方法可能会掩盖此类行为。我们通过检查在同一地理位置内供应无铅汽油的不同品牌的批发和零售汽油价格之间是否不匹配，为文献做出了贡献。为此，我们研究了石油或批发汽油价格变化引起的上游冲击对澳大利亚最大城市悉尼672个加油站的零售汽油价格的影响。我们发现，对于紧邻的竞争对手较少的站点，直通参数要低得多。如果半径不超过5公里的加油站少于13个，或者距离10公里之内的加油站少于33个，则不论其品牌如何，它们对批发汽油价格或原油价格变化的反应变得越来越不敏感。我们的发现提高了市场透明度，并为监管机构提供了一条经验法则，使他们能够更有效地监控无铅汽油市场。