Australia's competition regulator has rejected plans by Caltex to take over 302 Mobil service stations.
The Australian Competition and Consumer Commission says the $A300 million deal would have substantially reduced competition in specific areas, and and have a flow on impact in the wider retail fuel market, the ABC reports.
The competition watchdog was particularly concerned that an increased concentration of service station ownership in Brisbane, Sydney, Melbourne and Adelaide would inhibit more aggressive discounting.
Motoring groups have welcomed the decision.
Caltex and Mobil say they are disappointed, but Mobil still hopes a deal can go ahead.