Unfortunately, I'm not finding the numbers I need to get a good estimate. The important question is what portion of petroleum use winds up servicing those poor people versus the rest of the economy, because while it is certainly true that a small percentage increase in the costs of necessities hurts these people disproportionately, the money returned is a much greater portion of their income, and could very well dwarf the increased costs (indeed, this is what I would expect).

The very worst case, of course, is any who find themselves paying higher prices but unable for whatever reason to access the stipend.