Had a minute and found this
Some people argue that allowing more domestic offshore drilling would have little impact on oil prices. It is true that oil is a global commodity; however, after President Bush lifted the executive moratorium on July 14, 2008, and after Speaker Nancy Pelosi announced on September 23, 2008 that Congress would allow the congressional moratorium to expire, there were immediate price decreases. This is illustrated by the chart below:
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Economic theory predicts that the potential for greater future oil production should lead to price relief. It is true that lifting the moratorium could not immediately increase oil production from the affected areas, but other oil producers with excess capacity, such as Organization of Petroleum Exporting Countries (OPEC) nations, would have an incentive to produce more in the present once they believe that future U.S. output will be higher. This example from 2008 is one example of oil price relief because of potential future oil production.
Institute for Energy Research | Why Are Gas Prices So High?