Tacit collusion is a collusion between competitors, which do not explicitly exchange information and achieving an agreement about coordination of conduct. There are two types of tacit collusion – concerted action and conscious parallelism. In a concerted action also known as concerted activity, competitors exchange some information without reaching any explicit agreement, while conscious parallelism implies no communication. In both types of tacit collusion, competitors agree to play a certain strategy without explicitly saying so. It is also referred to as oligopolistic price coordination or tacit parallelism.

A dataset of gasoline prices of BP, Caltex, Woolworths, Coles, and Gull from Perth gathered in the years 2001 to 2015 was used to show by statistical analysis the tacit collusion between these retailers. BP emerged as a price leader and influenced the behavior of the competitors. As result, the timing of price jumps became coordinated and the margins started to grow in 2010.