There really isn't such a date anywhere in the foreseeable future. As long as we are willing to pay what it takes to get it. But even with the largely untouched oil shale, oil sands and tar sands, there's still oil to be found at ever deeper depths. At some point in the distant future, the cost of recovery will become SO high that no one will buy it. But before then it will have been replaced by other organic ( mostly renewable) sources.