I use Pocketbook. It opens just about anything - epub, mobi, pdf, pdb, and many more formats. Just get a book anywhere and copy it via USB. Or send it as an email attachment to your special address and it will download automatically. You can even replace the reading app with another relatively easily, if you want.
The reason for the 50 years of oil, as I heard it explained, is that this is how far ahead the oil companies plan. They look for enough oil to cover the timeframe they plan for. When they have that covered, they don’t look, until they need more. When they need more, they go and find it.