Here in Costa Rica every station has the same price, set by the government. They announce raises in advance so you can fill up one last time at the old price.
This Saturday gas will go from 565 colones to 600 colones per liter. As there are 3.8 liters per gallon and now 491 colones per $, this will mean a 27 cent increase per gallon from $4.37 to $4.64.
But they do wash your window, check fluids and tire air pressure for no extra charge if you ask. Happy with a small tip.