Here is an interesting article about fuel costs. Yes it is industry sponsored, but it still is pretty accurate.
Fuel Costs
The number 1 cause of increased gas prices is the price for crude on the world market. The oil companies are not going to sell the crude for less than the world market price.
In Venezuela the oil companies are owned by the government. The government has decided to sell gas for cheap. Just like the Iraq government does.
The price of gas at various gas stations is similar because all of the gas comes from the same refinery. Not because the oil companies collude.