Costco Warehouse (1st in Brisbane)

Finally, this much talk about shopping warehouse is in Brisbane. Opened just a week ago. After school, as a treat after term exams, MM, MJ and I decided to drive down to check it out. It is a warehouse of food and goodies, and naturally we did some of our shopping for the week. BTW LOOK at the sunset, blip taken on Samsung Galaxy S3 mobile phone.
Question: would Costco influence the prices of Woolies and Coles in the surrounding areas? Petrol prices are up to 20c/litre cheaper at Costco. You can only purchases Food and goodies packages in bulk (2 of some items or more) and worked out cheaper than buying single at other retailers; if these are what you use regularly. e.g.. 3L A2 Premium Milk $5.25 instead of $5 for 2L at Coles.