Even though oil prices have wobbled a bit over the past couple of months, optimism has returned to the oil market. Producers in the U.S. have ramped up investment spending to such a degree that Dave Lesar, the CEO of oil-field services giant Halliburton (NYSE: HAL), quipped last quarter that "animal spirits have broken free and they are running." Further, Lesar noted that "customers are excited again, and our conversations have changed from being only about cost control to how we can meet their incremental demand." However, when market conditions get this bullish, it's easy to forget what might go wrong.