Offshore Oildom tells the riveting story of the United States' quest to secure the oil riches of the sea. Drawing on a wealth of untapped sources, Tyler Priest reveals how the offshore oil industry emerged from an ambitious project to incorporate the ocean's submerged lands into the territory of the United States. These lands were frontier spaces, beyond traditional jurisdiction and control. Efforts to commandeer them for oil and gas extraction thus required new institutions of governance. From the titanic struggle over the tidelands starting in the 1930s to Project Independence in the 1970s, the process of establishing an offshore dominion of oil provoked intractable conflicts over money, values, and power. It pitted coastal states against their land-locked counterparts and captains of industry against federal civil servants and coastal communities. It stoked partisan and internecine warfare. It set off an international race to annex offshore territory, complicating U.S. foreign-policy objectives. It weighed on the minds of Supreme Court justices and troubled every occupant of the White House from Franklin Roosevelt forward. The modern environmental movement was born in opposition to offshore oil just as the 1970s energy crisis compelled the acceleration of drilling in the ocean. Creating and governing an offshore oildom involved nothing less than redrawing the territorial borders of the nation, rebuilding the political foundations of the U.S. energy system, and testing the environmental limits of resource extraction. This history is essential to understanding the tension between energy security and environmental protection in modern America.