The trend is your friend in oil's recent 30% slide. A safe trade would be to go short the US Oil ETF (USO) and long Halliburton (HAL). From a fundamental basis, Halliburton has more limited downside than the actual commodity. The other trade would be to go short the ethanol producers (PEIX or VSE) and long Halliburton. If you have an option account, consider buying puts in USO, VSE, PEIX.