Extremely difficult and expensive.
A tanker of crude oil has far more value than a tank of H2 would. That is, IF you could actually store the H2 long enough to transport it from say Iceland or wherever.
So we'll never be able to do it? Don't be daft molly - a H2 economy is possibly something that would happen in the long run - not least because it fits the current model of being able to drive somewhere and fill up, rather than wait to charge a vehicle. Also, if renewables are to become a larger part of the energy mix then H2 also represents the most plausible current tech for large-scale energy storage to even out the peaks and troughs.
Yeah but it's a lot easier to recycle water than it is petrol.
Not when it's evaporated, it's not.
And also not on the scale required to irrigate vast areas of semi-arid agricultural land to make it productive. And with climate change, demand for irrigation will increase. Most of this water is effectively mined - abstraction rates far exceed aquifer recharge. Typically we don't think about water in the UK because it rains a lot. Yet the SE is suffering from chronic water shortages.
Oil is but a sideshow by comparison. Food and water are the biggies, and as modern agriculture is dependent upon fossil-based energy both for working on farms, but also to make fertiliser, the cost of food will be squeezed from both sides. Fertiliser and fuel become scarce increasing food production costs, and limited water for irrigation increasing pressure on what were the more fertile, wetter areas. Then there's the transportation costs of said food.
If we can't afford the petrol to go for a day out to the beach that will be an inconvenience. When bread is over $20 a loaf, and you have to get your water from a rationed stand-pipe, then you have a problem.