There is also the fact that two thirds of service stations have their prices set by the station manager. One third of the retailers are managed by the refiners. The largest has 7% of the service stations. It is impossible to push prices up with only 7% of the market. But it is easy to push prices down: if even a single station decides to drop its prices, the market will follow.
On June 18th, 2007. See this statement in context.