I had heard several years ago that once oil got to $30 a barrel, it would be cost effective to extract from the oil shale in Colorado.
I take it that was just what in sales is called a BFC (Big Fat Claim) with no real evidence to support it.
Shell claims that their in situ retorting process would be cost effective at $30/bbl. After adjusting for inflation and salesman's hype, I think $60/bbl would be a good estimate for profitable extraction. The whole thing is still stalled by being wrapped up in government (read "environmentalist democrat") red tape.
There is enough kerogen recoverable using current technology to supply the entire current US demand for oil for over a hundred years.