What Is "Overseas Contingency Operations"? (OCO Defined)

Overseas Contingency Operations (OCO) was a US federal budget category — not a SIPRI-tracked spending figure — used from the early 2000s until 2021 to fund the wars in Iraq and Afghanistan and related counterterrorism operations outside the Pentagon's normal "base" defense budget. SIPRI's global dataset does not report a US OCO line item; the relevant scale reference on this site is the $2,740.0bn spent by 149 countries worldwide in 2025, the total within which US defense spending — historically the largest in the dataset — sits.

01 What Does Overseas Contingency Operations (OCO) Mean?

Overseas Contingency Operations, usually shortened to OCO, was the label the US government gave to funding requests for military operations judged to be temporary, war-related, and separate from the department's peacetime budget needs. Because OCO spending was requested and appropriated outside the normal budget caps that applied to the base defense budget, it functioned as a parallel funding channel: Congress could approve it with less friction against statutory spending limits, and the Pentagon could use it to cover costs tied directly to active combat operations.

The term is US-specific. It does not correspond to a category in the SIPRI Military Expenditure Database, which tracks total national defense spending by country and year rather than sub-national budget mechanisms. Readers who encounter "OCO" in a US budget document or news article should treat it as a historical accounting label, not a metric comparable to the world totals tracked elsewhere on this site, including the 2025 world rankings.

02 A Brief History: From the Iraq/Afghanistan Wars to Its 2021 End

OCO-style war funding emerged after the 2001 invasion of Afghanistan and the 2003 invasion of Iraq, when the US government began requesting large supplemental appropriations to cover combat costs that had not been anticipated in the regular defense budget cycle. The "Overseas Contingency Operations" name was formalized in the mid-2000s and used consistently through the following decade and a half, spanning the peak of US troop deployments in both countries and their subsequent drawdowns.

As US combat operations wound down — full troop withdrawal from Iraq in 2011, followed by the reduction and eventual 2021 withdrawal from Afghanistan — the rationale for a separate war-funding account weakened. The Biden administration's Fiscal Year 2022 budget request, submitted in 2021, eliminated the OCO designation entirely, folding any remaining contingency-related costs back into the base defense budget. Since then, the term has appeared only in historical or retrospective contexts.

03 Why OCO Existed: Off-Budget War Funding Explained

OCO existed largely as a budgetary workaround. US defense spending is normally constrained by statutory caps — most notably those set under the Budget Control Act of 2011 — that limit how much the base defense budget can grow year to year. War funding requests submitted under the OCO designation were treated as emergency or contingency spending and were exempt from those caps, giving policymakers a way to fund active operations without breaching the broader budget agreement.

• Cap avoidance — OCO spending did not count against statutory defense spending caps, unlike the base budget.
• Flexibility — Requests could be submitted and adjusted mid-year as operational needs in Iraq and Afghanistan changed.
• Separate accounting — Because OCO funding moved through a different appropriations track than the base budget, it was reported as a distinct line in US budget documents, separating war-related costs from the department's peacetime baseline.

04 How OCO Funding Compared to the Base Defense Budget

OCO funding was largest during the peak years of the Iraq and Afghanistan deployments and added a supplemental amount on top of the base defense budget in each of those years. As troop levels fell through the 2010s, OCO requests shrank accordingly, and by the final years before its elimination the category had become a much smaller supplement to the base budget rather than a major parallel funding stream.

This structural difference — one account subject to statutory caps, the other exempt — is what let OCO function as a separate funding channel alongside the base budget for as long as the designation existed.

05 OCO in Context: US Spending Within the $2,740.0bn World Total (2025)

SIPRI does not publish an OCO-specific figure, so the most useful citable anchor for scale is the world total itself. Summing SIPRI's country-level data for 2025 gives $2,740.0bn in military spending across 149 countries — the year's global backdrop against which any single country's defense budget, including the United States', should be read. US defense spending, historically the largest single national total in this dataset, sits within that $2,740.0bn figure; readers can see the full country-by-country breakdown on the 2025 world rankings page.

For a fuller picture of how glossary terms like OCO relate to the metrics tracked across this site, see the glossary.