The day before earnings, XOM was $84.75 or so due to a late day rally in the stock ahead of earnings. Stocks are valued based on the expected cash flows that they generate from now until the end of time discounted to a present value using an interest rate commensurate with the risk of the security. The riskier the security, the higher the interest rate used to discount those cash flows. Given that much of the price of oil and E&P companies is based on the current prices of oil and gas - which are finally showing how bubbly they have become, the risk in E&P stocks and major integrated oil companies like XOM have increased - which means that a higher interst rate would be appropriate for discounting the expected cash flows that XOM will receive in the future. Those cash flows are based on reserves. Those reserves are also dependent on the price of oil and gas. The higher the price, the more technology gets developed to extract the harder to reach oil and the more they will extract the tough to reach oil with current technology - e.g. many of the Canadian oil sand projects - see Suncor (ticker SU in both the US and Canada) or Canadian Oil Sands (Canadian ticker COS-U). Lower the price of oil and these companies are far less incentivized to extract oil from the oil sands. So, future earnings have been discounted more - this leads to the oft talked about concept of "multiple compression" where a stock's earnings today have not changed, but it price got smoked leading to a lower Price to Earnings ratio (P/E) (Another way for multiple compression to happen is for earnings growth to slow since one would be discounting smaller future cash flows).
Not only did the price of oil start to crack before XOM reported on July 31, but people still had high expectations that they would beat analyst estimates for earnings and guide to higher earnings. This did not occur. They missed and did not guide higher - so their growth slowed even though it was a record and it missed estimates - and their is higher risk in the underlying commodities that were driving the stock prices and earnings. All of these things lead to multiple compression and the stock got spanked.
Below is a chart for XOM going back 7 days. The first day has the run up in XOM in anticipation of earnings. The second day is after they missed and the rest is the tumble that ensued as oil tumbled. The second chart is the intraday price of oil over the last 20 trading sessions.
Happy trading...
Oil is fucking volatile - the close to close prices are volatile enough, but the intraday volatility is through the roof - far more than any average stock!!!