On average it isn't true. The average profit margin is 1.4% for gas stations in the US. Clearly the majority are not making much money on gas. Presumably that low average could mean for many gas is a loss leader.
not actually contra. Those extra cents selling at retail prices need a lot of volume to break even given employees, property taxes, maintenance.
That's why there is always something on the property to sell- convenience store, car mechanic garage, car wash, even whole restaurants sometimes.