Recall that the long-run value of a stock depends on the present value of its expected future free cash flows discounted at the WACC.
Locking in the cost of oil will cause an increase in stock price if and only if it causes the future expected future cash flows to increase, or WACC to decline.
Locking in the cost of oil that $80 will lower the riskiness of the expected future free cash flows but not the size because investors already expected a price of $80.
WACC will change only if locking in the cost of oil causes a change in the cost of debt, or equity, or target capital structure.