They are locked in shale rock.

William J. Culbertson has written:

'Evaluation of retorted oil shale as a liner material for retorted shale disposal sites' -- subject(s): Oil shale reserves, Rocks, Sedimentary, Sedimentary Rocks

We still have some decades of oil reserves yet, much of which is in the form of shale oil. We continue improving shale oil recovery techniques so that some of the reserves once considered unrecoverable may now be claimed.

As for coal, we have several centuries of supply of it, at current consumption rates. The wisdom of liberating all the carbon trapped in coal into our atmosphere in the form of CO2 is, however, highly questionable.

Shale oil is an oil distilled from shales and used as fuel

No. Oil is a non-renewable resource, although there is plenty of it around. The problem is, that a large part of known oil reserves are in shale or sand, and it would take more money to get the oil out than you could sell it for.