A real options theory—in its classic formulation—suggests that firms invest less during times of high uncertainty, that is, uncertainty depresses investment. However, several theoretical extensions predict that the relationship between investment and uncertainty may be non-linear, or even non-monotonic, when classic model assumptions are violated. Some model parameters either reinforce or weaken the negative effect of uncertainty on investment, while others distort the investment-uncertainty relationship, making it follow an inverted U-curve. This paper is a first—to my knowledge—attempt to identify the factors affecting investment from various streams of theoretical literature on investor choice and uncertainty, and to assemble them in a single empirical framework. By employing a dynamic panel of oil company data and implied volatilities as measures of uncertainty, I am able to examine the impact of uncertainty on investment and the effect of several factors on the investment-uncertainty relationship. I obtain evidence in support of several predictions from the theory. Both economy-wide and firm-specific types of uncertainty, as well as financing constraints, are found to adversely affect investment, while industry-wide uncertainty has an ambiguous effect, depending on the level of output price. In tests for non-linearity in the investment-output price volatility relationship, I find that output price, firm size and its risk management ability weaken the investment-uncertainty relationship. On the other hand, market imperfection, financing constraints, the firm’s maturity and its risk aversion re-enforce the negative effect of uncertainty. In addition, adjustment costs seem to be considerable, as firm investment reacts to changes in macroeconomic conditions with a noticeable delay.