Why does Shell petrol cost more than other companies ?

[tot3ntanZz]

I filled at the shell pump for 109 rs and found out at an hp pump later that the rate was 104 rs

I had initially thought the rates went up again sometime in the last two weeks and I hadn't noticed but it didn't and shell is just selling 4rs more expensive than the government rate

Are they allowed to do that ? And I filled the normal one not the shell v-power which was 119 rs displayed in that petrol pump