| Clue | Source | Date |
|---|---|---|
| Source of fuel and soil mixed well (3,5) | ||
| Rock from which fuel may be extracted | The Times Concise | 08 Feb 2019 |
| Rock source of fuel | Newsday | 01 Feb 2019 |
| Sedimentary energy source | Newsday | 22 Jun 2018 |
| Western Colorado fuel source | The Washington Post | 12 Jul 2016 |
| Certain fuel source | ||
| Crude alternative | ||
| Sedimentary fuel source | ||
| Sedimentary fuel source |