I don't want to get into the politics of gasoline prices but...Venezuela is a huge oil producing country and my understanding is that they basically try to keep their economy going better by pricing gas at about what it costs to produce. Mexico on the other hand, is also a big oil producer and there is only one big gasoline retailer (Pemex-which I think may be gov't owned). Gas there was more like $3.25/gallon back in January, when it was about $2 here. Ironically, the stations closest to the US border were about the same as US prices - I guess because they had to compete.
It cost us way more to drive to the Guatemalan border than it would have to fly -maybe even first class. Unfortunately, that pretty much rules out driving down to fill up (unless you can get a ferry from Miami
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Oh yeah, and compare that with most of Europe where it's somewhere between $5-8/US gallon-although some of that huge price is due to the weakness of the US$ (some of our UK friends can chime in here with something more specific). There's a pretty sizeable movement in the UK toward converting cars to run on a natural gas instead of gasoline.
Can you tell I like to travel a lot?