Low oil prices, if sustained, could mark the beginning of a long-term drop in upstream oil and natural gas investment. Oil prices reflect supply and demand balances, with increasing prices often suggesting a need for greater supply. Greater supply, in turn, typically requires increased investment in exploration and production (E&P) activities. Lower prices reduce investment activity.Overlaying annual averages of the domestic first purchase price (adjusted for inflation) on oil and natural gas investment reveals that upstream investment is highly sensitive to changes in oil prices. Given the fall in oil prices that began in mid-2014 and the relationship between oil prices and upstream investment, it is possible that investment levels over the next several years will be significantly lower than the previous 10-year annual average.Oil production is a capital-intensive industry that requires management of existing production assets and evaluation of prospective projects often requiring years of upfront investment spending on exploration, appraisal, and development before reserves are developed and produced.