In partial answer to Sid Shahinian's questions I can offer the following few insights. Several years ago I worked on a tug, which periodically barged gasoline to St. Thomas. We brought gasoline from the Philips 66 refinery in Guayama PR, not Hovic as was (and is) popularly believed. I was given to understand that this was because of slight fluctuations in the rack rate at the time.
The price we charged the customer (through an agent) for the voyage amounted to approximately 5 cents per gallon on the 7000 barrels of our cargo. That cargo was then tanked by a distributor, who must apply a mark-up to the product to cover the many costs of tankage (including, one hopes, the cost of EPA compliance.) St. Thomas and St. John are at somewhat of a disadvantage in that they must pay this additional tankage cost, which is considerable on the relatively small volume of fuel that they consume. We were told that there was another "middleman" or distribution agent of some sort between the supply line and the pump. Each of these stages of distribution added their own cost and profit to the price per gallon.
Still, at the time (and it appears that little has changed) we could not with our best guesses account for more than about half of the cost-per-gallon disparity of gasoline between St Croix and her sister islands.
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