Five brands, one price

One moves, four follow

Over 143 price changes, all five brands matched within a week 90% of the time, and by the same amount in 83% of those. They moved on the same day only 1.4% of the time. Shell is the brand most often out in front.

Who goes first

In each complete episode, the number of days after the first move that each brand matched it. When one brand moved alone, it was Shell 37 times, Esso 17 and Caltex 12. PetroChina and Sinopec almost never go first.

Up 110 times, down 33

The median increase was HK$0.20 a litre and the median cut HK$0.10. In 2023 and 2024 together there were 17 increases and no cuts, while the price of imported petrol fell.

Where the money goes

Hong Kong imports all its petrol, and the duty has been HK$6.06 a litre since 1998. What is left after the import cost and the duty pays for storage, delivery, stations, land and profit. On the posted price it averaged HK$8.76 a litre in the first twelve months of this record and HK$19.03 in the last twelve. From January 2023 to December 2025 the posted price went from HK$23.09 to HK$28.89 while the import cost went from HK$5.23 to HK$4.29.

Walk-in discounts grew as the posted price rose. The average across the five brands went from HK$2.44 a litre in the first year of archived pages to HK$5.52 in the last. On the average price after that discount, the margin over import cost and duty still went from HK$6.74 to HK$13.11. Card and loyalty discounts go deeper and are not in the data.

Rockets and feathers

When the world price of gasoline changes, how much of the change reaches the pump, and how fast? In Hong Kong 30% of a rise shows up in the posted price within the week, against 7% of a fall. Los Angeles has the same lean but smaller; Perth, once its weekly price cycle is accounted for, has no significant lean.

What a crowded, transparent market looks like

Perth's retailers must tell the state's FuelWatch service their next day's price by 2pm and hold it for 24 hours, so every price is public, as in Hong Kong. The difference is the number of sellers. On a typical day the cheapest and dearest of Perth's 419 metro stations are 38 cents a litre apart, and the most common price is posted by only 23% of stations. Prices run a weekly cycle: the median is lowest on Tuesday (155.9 cents) and jumps on Wednesday (187.1 cents), the day prices are restored. That cycle is coordination of its own kind (Byrne and de Roos 2019), and it still ends in a price war every week.

What this shows, and what it does not

None of this is evidence of an agreement. Identical prices are what a few sellers with the same costs and fully public prices would produce on their own, and Hong Kong's Competition Commission said in 2017 that this kind of parallel pricing reveals very little by itself. US law asks for more than parallel conduct before inferring a conspiracy (Bell Atlantic v. Twombly, 2007), and Hong Kong's First Conduct Rule likewise targets agreements and concerted practices.

What the screens add is that the patterns come together and last: a stable leader and followers, increases that outnumber cuts more than three to one, faster pass-through of rises than falls, and a margin that took HK$10.27 of the HK$12.94 rise in the posted price. The data that would separate cost from conduct are station operating costs and rents, the timing of each brand's price notices, and the full discount terms by date. The Consumer Council collects some of these; none are published as data.

Limits: the open-data record starts in April 2020. Day-level timing depends on when the archive copied the file. The import price is a monthly average. The margin is gross of storage, delivery, station costs and rent.