Supply & demand is the biggest reason. We have plenty of oil here, but don't want to use it for various reasons. Every one else has paid outrageous amounts $ for fuel for years, it's our turn. The Arab (OPEC) nations aren't fond of the US support of Israel, so that puts us in the middle. I can't recall the last time we built new refineries, that limits the amount available. The biggest reason for higher prices, China. 30-40 years ago China was a pure "communist" country. You had what the government said you could have. China now produces everything under the sun. They have a lot of money, & a lot of people, & they (along with India) have many vehicles, & they all need fuel. Years ago if the US. had said we won't be buying oil from OPEC, they would have lost their biggest customer. Today they hold the advantage of having plenty of consumers.
Supply and demand usually cause oil price movements. Supply side: under-exploration, under-production, OPEC quotas, hurricane or natural disaster interruptions, over-regulation, and government policy all affect oil production. Transportation costs can increase thus causing costs (finished) to increase. Local and state taxes, carbon offsets, as well as regulatory impediments, also play a large part in costs. And demand has increased as China and other third-world countries increase their economies. Greed has a little to do with it, but it's also greed on the part of government: they get more in taxes than oil companies get in profit.